Tom, clean up the broken glass _________ someone walks on it.
The reason for his success is ______ he worked very hard.
Don’t try to cheat the taxman(税务人员); you’ll never ______it.
The chairman asked me to ______my speech to 20 minutes.
Seeing the enemy, Gary was behaving as though nothing ______.
—Who______ it be that is knocking at the door? —It ______ be Father, but I’m not sure.