单项选择（每题1分）
We must think twice _____ we make the final decision.
| A．when | B．while | C．until | D．before |
-Jenny took the 8：00 bus to Guangzhou this morning.
-Really? He＿＿the 9:00 train. It's much more comfortable and safer to travel by train.
| A．could have taken | B．should take |
| C．must have taken | D．can take |
Junk messaging has been a headache for years, ＿＿the action taken by the authori-ties has not yet produced the results expected
| A．as | B．but | C．so | D．before |
Most museums are just for looking. But today some of them have things for you to touch.The ＿＿say,“＿＿”
| A．signs; Do touch | B．notices; To touch |
| C．signals; Be touching | D．signs; No touching |
After chatting online for along time, Mary looked up, ＿＿that it was 11：00 pm, long past her usual bedtime.
| A．to see | B．saw | C．seeing | D．seen |
He is a strict but kind teacher, ＿＿my son loves and respects.
| A．one | B．he | C．the one who | D．he who |