A good friend from I was born showed up at my home right before I left for Beijing.A. howB

问题补充：

A good friend from I was born showed up at my home right before I left for Beijing.

A. how

B. whom

C. when

D. which

答案：

A. how

B. whom

(答案→)C. when

D. which

解析：考查定语从句：因为这句话的意思是：在我正要离开北京时我出生时就开始关系很好的朋友出现在了我家里。强调的是个时间的概念，从出生时就关系很好了。用介词from+when引导定语从句，选C。