By the time he was twelve, Edison _______ to make a living by himself.
| A．has begun | B．began | C．had begun | D．had been beginning |
31. I was just about to go to bed last night ______ the telephone rang.
| A．while | B．when | C．as | D．before |
30. The world is ______ seven continents and four oceans.
| A．made up of | B．make out of | C．made from | D．made in |
25. ---You’ve missed such a good chance. ---Yes, I that job the boss offered me.
| A．must have taken | B．must take | C．should have taken | D．should take |
23. He is always full of ______ as if he never knew tiredness.
| A．strength | B．spirit | C．force | D．energy |
22. One learns a language by making mistakes and ______ them.
| A．correct | B．corrects | C．correcting | D．to correct |