Professor Jordon is well known for his _____ into the habits of the common housefly.
| A．examination | B．introduction |
| C．research | D．expression |
________ is often the case with old people, my grandfather is fond of doing morning exercise.
| A．As | B．Which |
| C．What | D．It |
It hasn't been made clear ________ the new underground line is to be open to traffic.
| A．when | B．that |
| C．what | D．where |
What impresses me most is ________ he appears in front of others, he wears a sincere and charming smile.
| A．what | B．which |
| C．that where | D．that whenever |
It is announced that big prizes will go to ________ finishes the assignment on time.
| A．whom | B．who |
| C．whomever | D．whoever |
The pupils were playing games in the classroom ________ a gunman entered and began shooting wildly at them.
| A．while | B．when |
| C．as | D．before |