Air and the sun's rays create much distortion, and whatever tends to _____ their influence is useful to the astronomer.
| A．exclude | B．eliminate | C．extinguish | D．impose |
. The reason ________ he referred to for his success is ________ he always working hard.
| A．why, that | B．why, because | C．that, that | D．that, because |
. The teachers hope the little ________ has been learned will be useful when they leave school.
| A．that | B．what | C．knowledge | D．which |
. “This is a window, ________ the sun comes in.” said the lady to her baby.
| A．where | B．which | C．by which | D．through which |
. Living in the western part of the country has its problems, ________ obtaining fresh water is not the least.
| A．with which | B．for which | C．of which | D．which |
. These students will graduate from the university next summer, ________ they will have studied here for four years.
| A．by then | B．by that time | C．by the time | D．by which time |