More bison were killed．The bison population is thought ______ from 60 million to just a few hundred between 1850 and 1910.
| A．to have fallen | B．having fallen |
| C．to fall | D．falling |
Stand closer______ you'll be able to see it better.
| A．or | B．while | C．but | D．and |
The teacher never wears anything other than a suit _____ the season.
| A．whatever | B．wherever | C．whenever | D．however |
______ there is a snowstorm or other bad weather ,the bus always comes on time.
| A．Because | B．if | C．When | D．Unless |
“You can’t have your football back ____ you promise not to kick it at my dog again,” the woman said firmly.
| A．until | B．when | C．since | D．because |
Entering the house we found him lying on the ground with his mouth ______ and eyes______.
| A．open ; close | B．opened ; closed | C．opened ; close | D．open ; closed |