[求助] one grammar puzzle

Fossils, traces of dead organisms found in the rocks of Earth's crust, reveal_______ at the time the rocks were formed.

A.  what was like

B. what life was like

answer: B

请帮忙分析句子的结构，为什么选B, 谢谢！

考点宾语从句

reveal 后应该接名词或名词性从句 ，以what引导的宾语从句后接完整的句子，而且不倒装