It was not immediately obvious water was to be fundamental to the development of life.A.

问题补充：

It was not immediately obvious water was to be fundamental to the development of life.

A. what

B. that

C. when

D. why

答案：

A. what

(答案→)B. that

C. when

D. why

解析：It作形式主语真正主语为that从句，that只起连接作用不做成分。句意：水注定会成为生命发展的基础还不明显。