You can use daagh's methodology/reasoning but I think that there is a much simpler way to look at the question. Take note of the bolded portion of the question below. The underlined portion of the list that you are correcting has to contain
two out of the
three basic questions. Looking at the answer choices in this way first is the easiest way to do this problem in my opinion.
Any theory of grammar should answer
three basic questions: what constitutes knowledge of grammar, how
it is acquired, and how it is put to useit is acquired, and how it is put to use
the correct answer/in test conditions I'd mark that this answer choice is possible and quickly check the others to make sure it is the best choiceis knowledge of grammar acquired and how put to use
2/3 basic questions! but does not make grammatical sense - wrongit was acquired and put to use
2/3! but it links the last two questions together and breaks parallelism - wrongthe acquisition of it is put to use
links the last two together in the same fashion as above - wrong!the knowing of it is acquired and how it is put to use
2/3 but it is not grammatically correct - wrong