—Who______ it be that is knocking at the door? —It ______ be Father, but I’m not sure.
With so much homework to do, _________to play football.
_________ with the size of the whole earth, the biggest ocean does not seem big at all.
I recognized him_________ I saw him in the crowd.
—Li Ming went abroad in 2000. —No wonder. I ______ him ever since.
______ difficult the problem was, he tried his best to solve it.