1 . That was written in 1946, ________ the education system has undergone great changes.

A．when

B．during which

C．since when

D．since then

2 . We will put off the sports meet until next week, _________the weather may be better. （用适当的词填空）

4 . We will put off the picnic in the park until next week, ___________the weather may be better.

A．where

B．when

C．whom

D．which

5 . The human has entered the AI era, ________ robots are used in ordinary life, bringing great convenience to people. (用适当的词填空)

6 . I didn't become a serious climber until the fifth grade，________ I went up to rescue a kite that was stuck in the branches of a tree. (适当形式填空)

7 . We will put off the picnic in the park until next week, ________ the weather may be better.

A．that	B．where
C．which	D．when