问题
选择题
—What's behind the door?
—There must be a dog _____ behind it. [ ]
A. to sit
B. sit
C. sitting
D. to sitting
答案
答案：C
搜题请搜索小程序“爱下问搜题”
—What's behind the door?
—There must be a dog _____ behind it. [ ]
A. to sit
B. sit
C. sitting
D. to sitting
答案：C