By the time he realizes he ______ into a trap, it’ll be too late for him to do anything about it．
A．walks B．walked C．has walked D．had walked
—Is there anything wrong , Bob? You look sad．
—Oh, nothing much．In fact, I ______ of my friends back home．
A．have just thought B．was just thinking
C．would just think D．will just be thinking
The country has already sent up three unmanned spacecraft, the most recent ______ at the end of last March．．
A．has been launched B．having been launched
C．being launched D．to be launched
—Where did you get to know her?
—It was on the farm ______ we worked．
A．there B．that C．where D．there
______ I really don’t like art, I find his work impressive．
A．As B．Since C．If D．while
______ worries me the way he keeps changing his mind．
A．This B．That C．What D．It
