What provides a powerful way to measure geologic time?

Dating

At a glance, we identify a Subject and main verb in the original sentence.Also, the main verb is in simple present for (ends in -S). This leads us to anticipate a missing phrase or some form of missing adjective. It is not letter D because the main verb of the sentence ends in S. It is not letter A because we already have a main subject, and we do not need to repeat it with a pronoun. It is not letter B because dates ends in an S also, and we already have a main verb in this form. The correct answer is letter C.