You must notice ______ the emergency exit is when you enter the building.
| A．which | B．where | C．what | D．in which |
________ is known to all is that effective measures should be taken to deal with the problem of the overexploitation of our resources.
| A．What | B．It |
| C．As | D．Which |
I think you should work harder ________ you are satisfied with the way things are.
| A．if | B．when |
| C．since | D．unless |
．Ram explained to his mother ________ he would get home late that night because of extra work.
| A．that | B．which |
| C．what | D．whether |
Air pollution is getting more and more serious, so we must take action ________ it is too late.
| A．before | B．after |
| C．until | D．when |
Sarah Brightman, ________ will fly to space in 2015, is the first woman to fly there in the field of music.
| A．who | B．that |
| C．which | D．whose |