1 . Mr. Smith owned this oil painting until the early 1990 s, ____________he gave it to his grandson.

A．which

B．when

C．where

D．who

2 . 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

3 . 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.

A．when	B．where
C．which	D．why

4 . The book was written in 1946, ____ the education system has witnessed great changes.

A．when

B．during which

C．since then

D．since when