The boy isn’t old enough ________ with the difficult problem by himself.
| A．deal | B．deals | C．dealing | D．to deal |
He arrived____ London ____ a cold winter night.
| A．at; at | B．in; on | C． in; in | D．\; on |
When I walked past her room, I heard her _______ an English song.
| A．singing | B．was singing |
| C．sang | D．is singing |
Keep the machine _______, and you will know how it works.
| A．run | B．to run | C．running | D．runs |
—What was Tom doing _______ it was raining?
—He was doing his homework in the bedroom.
| A．since | B．while | C．when | D．if |
Yesterday, a man said he saw _______ UFO in the park. The police are looking for _______ UFO now.
| A．an; the | B．the; the |
| C．a; the | D．the; an |