Learning is not always fun. It can actually be quite ________.

Learning is not always fun. It can actually be quite ________.
A、amateur
B、temporary
C、scientific
D、frustrating
【正确答案】：D
【题目解析】：amateur业余的；temporary暂时的；scientific科学的；frustrating令人沮丧的
句意：学习并不总是有趣的。这实际上是相当令人沮丧的。