【题目】______ is often the case with children, Amy was better by the time the doctor arrived.
A.It
B.That
C.What
D.As

【答案】D
【解析】句意：正如孩子们普遍的现象，当医生到来时Amy身体好多了。这是一个非限制性定语从句，先行词是整个主句，关系词在从句中作主语，意思是：正如，像……一样，用as，故选D。