请教9808的两道语法题

yogurt

12.--- that distinguish human beings from mother primates are related to the ability of people to stand upright and walk on two legs.
(A) Many of the physical characteristics
(B) Of the many physical characteristics
(C) The physical characteristics
(D) There are many physical characteristics
答案是A,但C为什么不选呢?好像也对啊?
1 8. Because the diamond is the hardest naturally substance, it is
           A                                                 B
used in industry for to cut, grinding, and boring other hard materials.
                                 C                                                 D
naturally 作为副词不是不可以修饰名词的吗?