Correct Answer: A

Rationale: The correct answer is A: 'the students watched the snow begin to fall.' In this sentence, the structure is correct with the subject 'the students' followed by the verb 'watched' and the object 'the snow begin to fall' in a grammatically appropriate manner. Choices B, C, and D have issues with verb tense agreement and sentence structure, making them grammatically incorrect. Choice B changes the active voice to passive, choice C lacks a verb for the subject 'snow,' and choice D does not complete the action initiated in the introductory participial phrase.

Correct Answer: B

Rationale: The correct word that should replace 'among' in the sentence is 'between' when referring to a distinction between two things. 'Among' is used when referring to more than two items or when the items are part of a group. In this context, 'between' is more appropriate as there are only two treatment protocols being compared.

Correct Answer: A

Rationale: The correct answer is 'Is.' In this sentence, the subject 'picking up groceries' is singular, so it should be followed by the singular form of the verb 'to be,' which is 'is.' The verb should agree with the subject in number. 'Am' is incorrect as it is the first person singular form, 'Is it' creates an unnecessary question structure, and 'Are' is plural, not matching the singular subject. Therefore, 'Is' is needed to make the sentence grammatically correct.

Correct Answer: B

Rationale: 'Presents' is the correct choice here. The sentence requires a verb that indicates the condition appearing with a symptom. In medical terminology, when a condition 'presents' with a symptom, it means that the symptom is a noticeable feature or indication of the condition. Therefore, 'presents' is the appropriate verb to describe how the condition manifests itself with vertigo. The other options do not fit the grammatical structure of the sentence.

Correct Answer: C

Rationale: The correct word is 'too,' which indicates an excessive amount. In this sentence, 'too high' describes the fever being excessively high, making it difficult for the child to lie comfortably. The other options do not fit the context: 'to' is a preposition, 'much' describes quantity but not excessiveness, and 'more' indicates a comparison, which is not relevant here.