A huge amount of oil was spilt on the East Sea, the causes of are still under investigation.
A. it
B. that
C. which
D. whom
网友回答
A. it
B. that
(答案→)C. which
D. whom
解析：句意为：大量的石油在东海泄漏了，这次事故的原因还在调查当中。此题目是在考查非限制性定语从句的用法，which指代的是前面的整件事情，且前有of介词，能用于介词之后有which whom而此题目中前面指代的是事情，所以不能用whom.而that不可引导非限制性定语从中，故答案为C。