（ ）We don't know ______.A.how to do B.which to do C.what to do D.where to do
问题描述：
（ ）We don't know ______.A.how to do B.which to do C.what to do D.where to do
答
C
A与D中的HOW ,WHERE 都是疑问副词,不能作宾语,故排除,而B中的WHICH后应该有名词,也错