Some people who are very intelligent and successful in their fie

Some people who are very intelligent and successful in their fields find ________difficult to succeed in language learning.
A、which
B、how
C、that
D、it
【正确答案】：D
【题目解析】：本题考查it做形式宾语。句意为：一些在自己领域才智过人并且非常成功的人发现，在语言学习上取得成功是很困难的。