The invention of artificial hearts marked a turning point in the battle ________ heart disease.
| A．among | B．for |
| C．against | D．between |
He observed a stranger __________ around the store at midnight.
A, wandering B. to wander
C. wander D. to be wandering
My sister, an inexperienced rider, was found sitting on the bicycle __________ to balance it.
| A．having tried | B．trying | C．to try | D．tried |
We came home after our holiday only __________ our pet dog injured.
| A．found | B．to be found | C．find | D．to find |
Start out right away，__________ you'll miss the first train.
| A．and | B．but | C．or | D．while |
Not only __________ polluted but crowded.
| A．was the city ； were the streets |
| B．the city was；were the streets |
| C．was the city ； the streets were |
| D．the city was ； the streets were |