谁能帮我解释一下这几道定语从句题?

谁能帮我解释一下这几道定语从句题?
这些道题选哪一个?为什么?
70.Do you understand the theory ______
A.that how the living things came into being
B.how did the living things come into being
C.of how the living things come into being
D.of how did the living things come into being
77.All of the plants now raised on farms have been developed from the plants _____ wild.
A.once they grew
B.they grew once
C.that once grew
D.once grew
3.Don’t trust such men _____ praise you to your face.
A.as B.who C.that D.which