Explanation
Choice D is the best answer. The convention being tested is fragmentation, which refers to a group of words that is not a complete sentence but is punctuated as one. A complete sentence requires at least a subject and a verb, and this choice supplies the clause with the past tense verb “helped” to perform the action of the subject “her detailed plans … and her process of running tests.”
Choice A: “To help” is a to-infinitive and therefore cannot serve as the main verb of the sentence.
Choice B: “That helped” is a relative clause and therefore cannot serve as the main verb of the sentence.
Choice C: “Helping” is a present participle and therefore cannot serve as the main verb of the sentence.
✨ Expert's Tip ✨
In order for a group of words to constitute a complete sentence, it must have a subject and a verb. Otherwise, it is a sentence fragment.