We will have no water to drink _________ we don’t protect the earth.
A. until B. if C. unless
Are you _____ in these _____story books.
| A．interested. interesting | B．interested. interested. |
| C．interesting. interested | D．interesting. interesting |
——Who watered the flowers beside the window?
——Helen ____________.
| A．Did | B．Do | C．did | D．does |
It is _______ unusual thing for us to find ________ UFO.
| A．a; a | B．an; an | C．a; an | D．an; a |
It takes me two hoursmy homework every day.
| A．doing | B．to do | C．did | D．does |
I often saw the boysin the river.
| A．swam | B．swimming | C．to swim | D．swim |