Twenty-five percent of the water in this river _____ dirty in the past.
A. is B are C. was D. were
You will achieve nothing you work hard.
| A．if | B．unless | C．when | D．that |
I met a good friend of mine while I on the street.
| A．walks | B．walk |
| C．was walking | D．am walking |
---You have found your lost umbrella, haven’t you?
----Yes.I it behind the door this afternoon.
| A．have found | B．will find | C．found | D．looked for |
----What do you think of Tom’s speaking?
----No one does in our class.
| A．good | B．better | C．well | D．best |
We didn’t go home the old man was sent to the hospital.
| A．until | B．when | C．while | D．after |