Question

a recent study showed that gene therapy was effective in combating mitochondrial diseases in mice; the research team plans to continue to study it. which choice makes the sentence grammatically acceptable? a no change b them. c they. d other applications of gene therapy.

Explanation:

• Analyze Option A: The original "it" is ambiguous. The first part talks about gene therapy's effect on mitochondrial diseases in mice, so "it" is unclear if it refers to gene therapy, mitochondrial diseases, or the study. So A is incorrect.
• Analyze Option B: "them" is a plural pronoun. But there's no clear plural antecedent that fits. The main subjects are "gene therapy" (singular) and "mitochondrial diseases" (plural), but the context of "continue to study" doesn't logically fit "them" (mitochondrial diseases as the thing to study next, since the study already showed gene therapy's effect on them). So B is incorrect.
• Analyze Option C: "they" is a subject pronoun, but we need an object pronoun here (since "study" takes an object). Also, the antecedent issue remains. So C is incorrect.
• Analyze Option D: "other applications of gene therapy" provides a clear and logical object for "study". The research team showed gene therapy works on mitochondrial diseases in mice, and now plans to study other uses of gene therapy. This makes the sentence grammatically and logically correct.

Answer:

D. other applications of gene therapy.