The reason ________ Mr．Wang didn’t join us was that his wife was ill．

The reason ________ Mr．Wang didn’t join us was that his wife was ill．

A.which

B.why

C.that

D.because

答案及解析： B

解析：

当先行词为the reason时，定语从句可能用that/why/for which来引导，在本句中，定语从句成分完整，选用why/for which来引导。