do you know if the man -by the door is mr.smith?sure.we have known each other for a long time.
问题描述：
do you know if the man -by the door is mr.smith?sure.we have known each other for a long time.
为何选B
A stand B standing C stood D stands
答
句意：你知道那位正站在门边上的男人是不是史密斯先生?
当然,我们很了解彼此
正站在：正在进行时,用standing