English is difficult________. Nobody can learn to use it in a few minutes.
| A．learning | B．to be learned | C．learned | D．to learn |
I can still remember that it is since the 1990’s, _____ we began to use cell phones,_______ the number of mobile users has greatly increased．
| A．while; when | B．when; what | C．before; that | D．when; that |
—I can never forget the day ___ we spent together in the summer camp．
—Well, especially the day _______it suddenly began to rain in the middle of the night．
| A．when; when | B．which; when | C．what; that | D．on which; when |
Every one of us must know this: _________ we live can we save the earth．
| A．by changing the way only | B．by only changing the way |
| C．only by changing the way | D．by changing only the way |
During the period of recent terrorist activities, people _____ not to touch an unattended bag．
| A．had always been warned | B．were always being warned |
| C．are always warning | D．always warned |
—What a great cook your sister is!
—Yeah! We ______ never have enough of her cookies．
| A．may | B．must | C．should | D．can |