Correct Answer: B

Rationale: The correct punctuation needed in the sentence is a comma. A comma should be placed after 'festivities' to separate the two independent clauses in the sentence: 'In addition to the hospital's regularly scheduled festivities' and 'the custodians celebrate with a party of their own.' The comma helps in improving the clarity and structure of the sentence by indicating a pause between the clauses. Choice A, 'Period,' is incorrect because a period would create two separate sentences rather than connecting the related clauses. Choice C, 'Apostrophe,' is incorrect as there is no need for an apostrophe in this context. Choice D, 'Semicolon,' is incorrect because a semicolon is used to join closely related independent clauses, which is not the case in the given sentence.

Correct Answer: D

Rationale: The word 'their' is used incorrectly in the sentence. The correct word should be 'they're,' which is a contraction for 'they are.' The sentence should say: The boys leapt up, happy to assist their favorite teacher. Choice A, 'leapt,' is correctly used as the past tense of 'leap.' Choice B, 'happy,' is also correctly used as an adjective to describe the boys' emotional state. Choice C, 'assist,' is appropriately used as a verb to show the boys' willingness to help.

Correct Answer: C

Rationale: The word 'understand' should be used instead of 'understands' to maintain subject-verb agreement. In this sentence, 'few' is a plural subject, requiring the plural verb 'understand' rather than 'understands.' The corrected sentence reads, 'but few truly understand the essay.' Choice A, 'pretends,' is used correctly in the sentence. Choice B, 'truly,' is also used appropriately. Choice D, 'essay,' is also correctly used in the sentence.

Correct Answer: C

Rationale: The word 'boys'' should be spelled as 'boys' in this context. The correct possessive form of the plural noun 'boys' does not require an apostrophe before the final S, which indicates possession. In this sentence, the intent is to show that the pranks belong to the four boys collectively, so the correct possessive form is 'boys' without the additional apostrophe.

Correct Answer: B

Rationale: In the given sentence, the word 'once' is used incorrectly. The original sentence implies that the professor was an intern in the hospital at a specific time in the past, not just once. The word 'formerly' would imply that the professor used to be an intern but is no longer. Therefore, 'once' is the incorrect word choice in this context. The other options ('professor,' 'intern,' 'hospital') are all used correctly in the sentence.