1. 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=in addition to the routine discharge of drilling mud and mineral salts, are what make offshore oil drilling environmentally risky.

请问E为什么不对呢？along with 后面要用are还是is呢？

其实你从along with 前有逗号，就可以大略知，它不能做“真实主语”

更进一步说，即使没有逗号，也应该用单数

将along with理解为插入语，你就应该明白了.