He had his camera ready ________ he saw something that would make a good picture .
Humans are destroying nature day by day, ________, of course, will cause punishment sooner or later.
The school _______ I visited the other day was not the one _______ I once studied.
Is this the reason____ at the meeting for his carelessness in his work?
You stepped into the lab with your shoes on? You’re _______ to take them off before you enter it.
—We could invite John and Barbara to the Friday night party. —Yes, ______ ? I’ll give them a call right now.