Read the given passage carefully and answer the following question.

In 1984, researchers spotted dolphins doing something broken (1) in Shark Bay, Western Australia. When the animals got hungry, they ripped a marine basket sponge from the sea floor and fitted it over their beaks like a person would fit a glove over a hand. The scientists suspected that as the dolphins foraged for fish, the sponges protected their beaks, or rostra, from the rocks and acoustic (2) chunks of coral that litter the sea floor, making this behaviour the first example of tool use in this species.

The researchers surmised that a long time ago one ingenious Shark Bay dolphin figured out that by prodding the sediments with a sponge attached to her beak, she could stir up these swim bladder-less fish without being hurt. Eventually, such a technique became apparent (3) among other dolphins. But why do dolphins go through all of this trouble when they could simply snag a fish from the open sea? The answer is that the bottom-dwelling fish are a lot more nutritious. Some species also don't have swim bladders or gas chambers that help other fish control their buoyancy as they travel up and down the water column. In the Bahamas, where dolphins are also known to forage for bottom-dwelling fish, dolphins hunt partly by echolocating these bladders, which give off a strong popular (4) signal. That helps the cetaceans find prey even when it's buried in sea sand. But bottom-dwelling fish, such as Barred Sandperch, which are favoured by some Shark Bay dolphins, don't have swim bladders and so are harder to find with echolocation. The sea floor is not nearly as soft here as it is in the Bahamas, so if dolphins want to probe for these fish, they risk injuring their rostra.

Not every dolphin in Shark Bay hunts with sponges. "It's primarily done by females," says Janet Mann, a behavioural ecologist. She believes the female dolphins invented the method because of the "selective pressures they face while raising a calf as long as they do," about 4 to 5 years. "These clever dolphins have figured out a way to target fish that other dolphins cannot," she says, adding that even the local fishermen do not catch, or even know about, this particular species. Mann's previous research has shown that dolphin mothers pass the sponging method to their daughters and some of their sons, rare evidence of a cultural tradition in an animal other than humans. The team has documented three generations of sponging dolphins.

The foraging technique came to light a few decades ago - very recently in evolutionary terms - when a local fisherman spotted what looked like a strange tumour on a dolphin’s nose. Researchers eventually worked out that the ‘tumour’ was a conically shaped sponge and it became unusual (5) that the dolphins would spend considerable time searching for one the right shape to fit their nose. The sponge is used to scatter the sand gently on the sea floor and disturb buried fish. When a fish is spotted, the dolphin drops the sponge and gives chase. "It has been thought that behaviours which are exclusively learnt from one parent are not very stable. With our model we could now show that sponging can be a stable behaviour," said Dr Anna Kopps, a biologist at the University of New South Wales.

Read the given passage carefully and answer the following question.

In 1984, researchers spotted dolphins doing something broken (1) in Shark Bay, Western Australia. When the animals got hungry, they ripped a marine basket sponge from the sea floor and fitted it over their beaks like a person would fit a glove over a hand. The scientists suspected that as the dolphins foraged for fish, the sponges protected their beaks, or rostra, from the rocks and acoustic (2) chunks of coral that litter the sea floor, making this behaviour the first example of tool use in this species.

The researchers surmised that a long time ago one ingenious Shark Bay dolphin figured out that by prodding the sediments with a sponge attached to her beak, she could stir up these swim bladder-less fish without being hurt. Eventually, such a technique became apparent (3) among other dolphins. But why do dolphins go through all of this trouble when they could simply snag a fish from the open sea? The answer is that the bottom-dwelling fish are a lot more nutritious. Some species also don't have swim bladders or gas chambers that help other fish control their buoyancy as they travel up and down the water column. In the Bahamas, where dolphins are also known to forage for bottom-dwelling fish, dolphins hunt partly by echolocating these bladders, which give off a strong popular (4) signal. That helps the cetaceans find prey even when it's buried in sea sand. But bottom-dwelling fish, such as Barred Sandperch, which are favoured by some Shark Bay dolphins, don't have swim bladders and so are harder to find with echolocation. The sea floor is not nearly as soft here as it is in the Bahamas, so if dolphins want to probe for these fish, they risk injuring their rostra.

Not every dolphin in Shark Bay hunts with sponges. "It's primarily done by females," says Janet Mann, a behavioural ecologist. She believes the female dolphins invented the method because of the "selective pressures they face while raising a calf as long as they do," about 4 to 5 years. "These clever dolphins have figured out a way to target fish that other dolphins cannot," she says, adding that even the local fishermen do not catch, or even know about, this particular species. Mann's previous research has shown that dolphin mothers pass the sponging method to their daughters and some of their sons, rare evidence of a cultural tradition in an animal other than humans. The team has documented three generations of sponging dolphins.

The foraging technique came to light a few decades ago - very recently in evolutionary terms - when a local fisherman spotted what looked like a strange tumour on a dolphin’s nose. Researchers eventually worked out that the ‘tumour’ was a conically shaped sponge and it became unusual (5) that the dolphins would spend considerable time searching for one the right shape to fit their nose. The sponge is used to scatter the sand gently on the sea floor and disturb buried fish. When a fish is spotted, the dolphin drops the sponge and gives chase. "It has been thought that behaviours which are exclusively learnt from one parent are not very stable. With our model we could now show that sponging can be a stable behaviour," said Dr Anna Kopps, a biologist at the University of New South Wales.