Correct Answer: B

Rationale: The correct punctuation needed in the given sentence is a comma after 'class.' This comma is necessary to separate the two independent clauses 'Do not be afraid to ask questions in his class' and 'he is very approachable and explains things well.' Commas are used to separate independent clauses when they are joined by a coordinating conjunction like 'and.' Choice A, 'Hyphen,' is incorrect as a hyphen is not needed to connect any words in the sentence. Choice C, 'Apostrophe,' is incorrect as there is no possession or contraction being indicated in the sentence that requires an apostrophe. Choice D, 'Semicolon,' is incorrect as a semicolon is not used to join two independent clauses in this context; a comma followed by a coordinating conjunction is more appropriate.

Correct Answer: B

Rationale: The word 'envelope' is used incorrectly in the sentence. The correct word should be 'folder,' as mentioned in the original sentence. An envelope is a flat paper container for a letter or documents, while a folder is a folded cover for papers or documents. 'Give,' 'whoever,' and 'replies' are all used appropriately in the sentence, so they are not the incorrect words.

Correct Answer: B

Rationale: The word 'their' is the correct possessive pronoun to use in this sentence because it indicates that the coats belong to multiple patients. 'Their' shows ownership by a plural group, which is the most suitable choice in this context. Choice A, 'his,' is singular and would imply that all the coats belong to one male patient, which is not the case. Choice C, 'them,' is a pronoun used for indicating objects or people and not possession. Choice D, 'theirs,' is a possessive pronoun but is used to refer to something that belongs to multiple people, not in this case where the coats belong to the patients.

Correct Answer: B

Rationale: The correct answer is 'itself.' The sentence is referring to the centrifuge, which is an object, not a person. Therefore, the word 'itself' is used to indicate that the centrifuge cannot run on its own; it requires constant attention. Choices A, C, and D are incorrect because they refer to a person or people, which is not suitable in the context of the sentence.

Correct Answer: B

Rationale: The word 'nevertheless' is used to show contrast or contradiction between two ideas. In this sentence, acknowledging the positive quality of being caring but stating that more training is needed presents a contrast. Therefore, 'nevertheless' is the appropriate word to bridge the two ideas together logically. Choices A, C, and D do not convey the intended contrast between the two parts of the sentence, making them grammatically incorrect in this context.