Correct Answer: B

Rationale: The correct answer is B: 'Let's eat, Grandma!' The comma is correctly used to separate the direct address 'Grandma' from the rest of the sentence. In choice A, there should be a comma after 'eat' to separate the direct address. Choice C is missing an apostrophe in 'Lets,' and there should be a comma after 'eat' to separate the direct address. Choice D incorrectly places a comma after 'Lets,' and there should be a comma after 'eat' to separate the direct address.

Correct Answer: D

Rationale: The teacher should advise the student that 'ain't' is a colloquial expression, and while it may be suitable in informal or conversational settings, it is not standard in academic writing. Using colloquialisms like 'ain't' in formal research papers can diminish the professionalism and clarity of the writing. Choice A is incorrect as the presence of a word in the dictionary does not solely determine its appropriateness in formal writing. Choice B is incorrect because the student's academic level does not justify the use of non-standard English. Choice C is incorrect as it focuses on the perceived uneducated sound of 'ain't' rather than its appropriateness in formal writing, which is the key concern for the research paper in question.

Correct Answer: C

Rationale: The correct answer is C because there is a tense disagreement in the sentence. The use of 'was' (past tense) and 'she's' (contraction of 'she is' present tense) creates an inconsistency in the verb tense. The sentence should maintain consistency either in past tense ('She was a gifted pianist, although she struggled with the piece for her upcoming concert') or present tense ('She is a gifted pianist, although she's struggling with the piece for her upcoming concert'). Choices A, B, and D are incorrect as the issue in the sentence is related to verb tense disagreement, not transition words, diction, or sentence completeness.

Correct Answer: A

Rationale: In this context, the word 'prodigious' is used to describe the Mayan pyramid at Chichen Itza. The tour group's nervousness about climbing its distant peak indicates that the pyramid is impressive in size and scale, invoking a sense of awe or grandeur. Therefore, the correct meaning of 'prodigious' in this context would be 'very large.' Choice B, 'Famous,' is incorrect as the sentence focuses on the size rather than the fame of the pyramid. Choice C, 'Very old,' and choice D, 'Fancy,' do not accurately capture the intended meaning of 'prodigious' as used in this context.

Correct Answer: D

Rationale: The correct spelling is 'indispensable,' which means absolutely necessary. In this context, it implies that his skill on the soccer field is crucial and vital for the team's success. Choices A, B, and C are incorrect due to misspellings that do not accurately convey the intended meaning.