12.   Chronic low-level leaking and the routine discharge of drilling mud and mineral salts present considerable environmental risk during offshore oil drilling.

(A) Chronic low-level leaking and the routine discharge of drilling mud and mineral salts present considerable environmental risk during offshore oil drilling.

(B) The reason offshore oil drilling presents a considerably environmental risk is because of chronic low-level leaking and the routine discharge of drilling mud and mineral salts.

(C) A considerable risk to the environment is presented during offshore oil drilling, where low-level leaks are chronic and the routine discharge of mud and mineral salts.

(D) Offshore oil drilling presents a considerable risk to the environment due to the fact of chronic low-level leaks, and mud and mineral salts are routinely discharged.（A）

(E) Chronic low-level leaking, along with the routine discharge of drilling mud and mineral salts, are what make offshore oil drilling environmentally risky.

请问NN，A 中risk 不需要复数形式么？ E 错在哪里？ 其中are what make.. 这样的用法可以么？

 E的那种along with 显然不是GMAC喜欢的类型. 他们更青睐于简洁的,清晰的对称结构.

而A中的risk,不知能否理解成一个抽象的名词...

我语文也烂,说点个人观点,还是请NN解释吧!!!