1 . It is true that tourism can benefit the local economy, but increased tourist numbers will also mean more cars and aeroplanes,           in turn means higher carbon emission and further destruction of environment.

A．that

B．which

C．as

D．when

2 . My mother was too busy to remember my birthday, ________ made me a little upset.

A．which

B．that

C．whom

D．what

3 . First aid techniques are often simple, ________ can be taught to people of all ages.

A．that

B．what

C．which

D．it