—Look！He's running so fast!
—Hard to ________ his legs were once broken.
| A．know | B．imagine |
| C．realize | D．find |
She was greatly shocked at the scene before her eyes. Never did she expect that local conditions___________be so awful.
| A．could | B．should | C．would | D．might |
Only when the villagers were faced with water shortage___ how serious the problem of water pollution was．
| A．did they realize | B．will they realize | C．they did realize | D．were they realized |
Only by practicing every day ___________ English well.
| A．can we learn | B．we can learn | C．did we learn | D．learn we |
Only when 1 was fourteen__________the importance of study．
| A．I realized | B．did I realize | C．had I realized | D．I had realized |
Only after the plane had taken off _________ that he missed his parents so much.
| A．he found | B．he had found | C．did he find | D．was he found |