问题
选择题
David can speak idiomatic American English and yet, _____ English, he doesn't know it at all.
A．how to teach
B．when it comes to teaching
C．when he teaches
D．however he teaches
答案
答案：B
when it comes to doing sth.是惯用法，意思是“当提到……的时候，”符合题意，而其它选项在逻辑上与上下文不符。