Quote:
(A) Chronic low-level leaking and the routine discharge of drilling mud and mineral salts present considerable environmental risk during offshore oil drilling.
Noting bad with A here, let's keep it.
Quote:
(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.
The use of "considerably" (instead of "considerable") results in strange meaning: now "considerably" modifies adjective "environmental". It does not make sense.
Quote:
(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.
Parallelism issue: full clause "low-level leaks are chronic" is not parallel to noun phrase "the routine discharge of mud and mineral salts"
"where" should be used to modify real places, not conceptual ones. So, it is better to use "in/during which".
Quote:
(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.
Parallelism issue: noun phrase "chronic low-level leaks" is not parallel to the full clause "mud and mineral salts are routinely discharged"
The meaning is slightly shifted: now it seems that environmental risk is caused by mud and mineral salts.
"due to" should explain the reason for nouns, not actions: "because of" will work better for this choice.
Quote:
(E) Chronic low-level leaking, along with the routine discharge of drilling mud and mineral salts, are what make offshore oil drilling environmentally risky.
S-V agreement error: singular subject "leaking" requires singular verb "is", not "are".
Only "and" makes compound subject; phrases "along with", "as well as", "together with", etc. do not make a compound subject and affect its singular/plural nature.
A is correct choice.