They kept trying _____ they must have known it was hopeless.
| A．if | B．because | C．when | D．where |
Most online classes let students learn _____ their own pace.
| A．at | B．to | C．from | D．by |
_____the size of the universe, some researchers believe that there is life beyond our planet.
| A．Consider | B．To consider |
| C．Considered | D．Considering |
The trains leave every 15 minutes; if you miss ____ , you don’t have to wait long for another.
| A．it | B．this | C．one | D．some |
Mr. Sawyer started his career at Stanford University, _____ he became Professor of Physics in 2002.
| A．which | B．where | C．when | D．that |
–Peter, do you know how to download the new software?
–Certainly. I _____ you the steps.
| A．show | B．am showing |
| C．will show | D．have shown |