It is well-known to us all that knowledge is __ treasure, but practice is ___ key to it.
| A．a, ∕ | B．a, the | C．the, the | D．∕ , the |
The engineer ________ my father works is about 50 years old.
| A．to whom | B．on whom |
| C．with which | D．with whom |
They arrived at a farmhouse，in front of ________ sat a small boy.
| A．whom | B．who | C．which | D．that |
The pen ________ he is writing is mine.
| A．with which | B．in which |
| C．on which | D．by which |
Can you lend me the book ________ the other day?
| A．about which you talked | B．which you talked |
| C．about that you talked | D．that you talked |
At the party，John made up a joke，________ people burst out laughing.
| A．on which | B．by which | C．at which | D．from which |