By the time he was ten, Edison _________ experiments in chemistry.
| A．had already done | B．already had done |
| C．was already doing | D．already did |
There are two in her family．（ ）
| A． |
child |
B． |
childs |
C． |
children |
I didn't know _____．（ ）
| A． |
what we could do |
| B． |
how we could do |
| C． |
what can we do |
How long is it since he _____this school？
He _____for three years．（ ）
| A． |
has left； has left |
| B． |
left； has been away |
| C． |
leaves； has left |
The lights is on．When you leave，please _____．
OK，I won't forget ____it．（ ）
| A． |
turn it off； to do |
| B． |
turn off it； doing |
| C． |
turn on it； to do |
It takes me half an hour _____playing the piano．How about you？
I usually spend 20 minutes ____it．（ ）
| A． |
practicing； on |
| B． |
to practice； in |
| C． |
to practice； on |