is often the case, the weather has turned out well as expected.
A. Which
B. When
C. What
D. As
网友回答
A. Which
B. When
C. What
(答案→)D. As
解析：考查非限制性定语从句：句意：这是常有的事，天气如所预期的那样变好了。As is often the case情况经常是这样的，as引导非限制性定语从句，指代主句的内容，在定语从句中as做主语，which可以引导非限制性定语从句，但是不能让在句首，选D。