In 1800, a group of adventurers set out on their exploring trip. Five days later, they came to _______ is now known as Quebec.

           A．what               B．which                 C．the place             D．where

---- Can you think of a case in which the ecology of an area is in balance?

  ---- Sure. You see, ______ an environment is undisturbed, the ecology of the area is in balance.

A．unless                        B．as                       C．though                D．where

The question _____ should do the work requires further discussion in the next meeting.

A. who                  B. that                   C. whom               D. why      

In 1969, _____ everyone had dreamed of happened the astronaut landed on the moon.

A. that                  B. what                C. which               D. as

Gaining knowledge and acquiring skills are the main purpose of school education, and therefore students should memorize _____ they are taught in class.

A. it                             B. what                        C. that                          D. all what