TOEFL Reading: ETS-TOEFL阅读机经 - 68QM7S1XDFO7LRJ5L$

According to paragraph 2, Lyell's strategy for estimation geologic dates was not very accurate for periods before the Tertiary Period party because A. Marine mollusks did not evolve until the Tertiary Period B. fossil records of the very distant past are incomplete C. there was not much agreement about how to identify or categorize earlier eras D. the duration of previous geologic periods was difficult to determine