请教几道语法题，特别请教xizzhu

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     c. what life was like    d. that life was like

请问：a.b.c各自有什么区别？was like 后面非要接个宾语吗？比如：life was like when..为何不行？

C is correct.    when you put A and D in this blank, the sentences do not make sense and  no meanings.

It is difficult for present-day readers       Sister Carrie was withdrawn from circulation at the turn of the century.

a. to understand the novel why         d. to understand why the novel

答案为ｄ，the novel　与　Sister Carrie　为同位语吗？yes.  可是ａ为何不对，ｗｈｙ引导的从句可以做定语从句修饰the novel吗？NO,

"understand why"  is a common expression.

The flowering of African American talent in literature, music, and art in the 1920’s in New York City became to know as the Harlem Renaissance.

答案为ｄ,怎么改：became to be known as  is correct.     became as known as is incorrect.