—Who left the door open?
— Oh, sorry. I _____ the door.
| A．ought to lock | B．should lock | C．ought to have locked | D．could lock |
Listening to music can be very enjoyable, but ________ can be appreciated unless you like it.
| A．nothing | B．something |
| C．everything | D．anything |
The cultural background of China is totally different from ________ of the US.
| A．one | B．that |
| C．these | D．those |
The teacher praised me for ________ progress I'd made, which was ________ great encouragement to me.
| A．the; / | B．the; a |
| C．/; a | D．/; / |
As ________ birthplace of Huaxia civilization, Xi'an is ________ city with a long history and abundant cultural relics.
| A．the; a | B．a; a |
| C．/; a | D．the; / |
University is ________ most worthwhile time of discovery and learning, and it is also ________ very enjoyable and valuable experience for every one of us.
| A．a; a | B．the; / |
| C．/; a | D．a; the |