The only complete sentence is “If you touch a flower in spring, you may get the yellow dust of pollen on your fingertips.” No other combinations exist for making a complete sentence.

The only complete sentence is “Musicians have to attune their instruments before playing to get the exact sound that they want or need.” No other combinations exist for making a complete sentence.

The only complete sentence is “The worker tried not to get angry, but he couldn’t help feeling annoyed at his rude boss.” No other combinations exist for making a complete sentence.

“Due to” adjoins the two phrases correctly, making the sentence grammatically correct and contextually coherent.

Option (a) "however" indicates a contrast or contradiction between the two phrases, which is not suitable here as we are looking for a connector that shows the cause-and-effect relationship.

Option (b) "therefore" indicates a consequence or conclusion, but it does not properly connect the two phrases in terms of cause and effect.

Option (c) "due to" is the correct choice. It indicates that the economic downturn caused by the pandemic is the reason for the company's plummeting profits. This connector establishes a cause-and-effect relationship between the two phrases.

Option (d) "despite" indicates a contradiction or unexpected outcome, which is not appropriate here as we are discussing the cause of the company's profit decline.

Option (e) "whereas" indicates a contrast between the two phrases, which is not the intended relationship in this context.

Therefore, the correct answer is (c) "due to."

“Thereby” adjoins the two phrases correctly, making the sentence grammatically correct and contextually coherent.

Option (a) "whereas" indicates a contrast or comparison, which is not suitable here as we are looking for a connector that shows a cause-and-effect or sequential relationship.

Option (b) "thereby" is the correct choice. It means as a result of or by means of something. In this context, it indicates that the researcher conducted extensive experiments, and as a result, they gathered substantial evidence to support the hypothesis.

Option (c) "such as" is used to provide examples, but it does not properly connect the two phrases in terms of cause and effect.

Option (d) "besides" indicates something in addition to or apart from something else, but it doesn't establish a clear relationship between the two phrases.

Option (e) "although" introduces a contrast or contradiction, which is not the intended relationship in this context.

Therefore, the correct answer is (b) "thereby."

“Thus” adjoins the two phrases correctly, making the sentence grammatically correct and contextually coherent.

Option (a) "yet" indicates a contrast or contradiction, which is not suitable here as we are looking for a connector that shows a cause-and-effect or sequential relationship.

Option (b) "leading to" indicates a result or consequence, but it doesn't properly connect the two phrases in terms of cause and effect.

Option (c) "as a result of" indicates a cause, but it doesn't directly connect the two phrases and is less concise than the correct option.

Option (d) "thus" is the correct choice. It indicates that the orchestra playing harmoniously resulted in the creation of a mesmerizing symphony that resonated with the audience's hearts. This connector establishes a cause-and-effect relationship between the two phrases.

Option (e) "indeed" indicates emphasis or agreement, but it doesn't properly connect the two phrases in terms of cause and effect.

Therefore, the correct answer is (d) "thus."

“Despite” adjoins the two phrases correctly, making the sentence grammatically correct and contextually coherent.

Option (a) "in view of" indicates because of a particular thing, or considering a particular fact; which is not suitable here as we are looking for a connector that shows a cause-and-effect or sequential relationship.

Option (b) "despite" is the correct choice. It means that the company's expansion plans were successful despite the initial setbacks they faced. This connector indicates that the second phrase contrasts with the first phrase in terms of expected outcome.

Option (c) "additionally" indicates some additional information, but it doesn't properly connect the two phrases in terms of cause and effect or expected outcome.

Option (d) "erstwhile" means former or previous and does not fit in the context of the sentence.

Option (e) "even" is used to emphasize something surprising or extreme, which is not appropriate here as we are discussing the relationship between the company's expansion plans and the eventual success.

Therefore, the correct answer is (b) "despite."

“Yet” adjoins the two phrases correctly, making the sentence grammatically correct and contextually coherent.

Option (a) "since" indicates for the reason that; because., which is not suitable here as we are looking for a connector that shows a contrast or unexpected outcome.

Option (b) "indeed" indicates emphasis or agreement, but it doesn't properly connect the two phrases in terms of contrast or unexpected outcome.

Option (c) "because" indicates a cause, but it doesn't properly convey the contrast between the rain pouring relentlessly and the determined hiker continuing to trek through the muddy trail.

Option (d) "yet" is the correct choice. It indicates a contrast or unexpected outcome. Despite the rain pouring relentlessly, the determined hiker continued trekking through the muddy trail. This connector highlights the perseverance and determination of the hiker despite the challenging weather conditions.

Option (e) "eventually" is used to convey in the end, especially after a long delay, dispute, or series of problems, but it is not the best choice in this context as it is too similar to the meaning conveyed by option (d) "yet."

Therefore, the correct answer is (d) "yet."

The verb "revolutionize" should be in the past participle form because it is being used in conjunction with the auxiliary verb "has." The correct past participle form of "revolutionize" is "revolutionized." All the other parts of the sentence are grammatically correct.

The adverb "drastically" is needed to modify the verb "improved." It should be used to indicate the manner in which the performance improved after hiring a new coach. All the other parts of the sentence are grammatically correct.