1 . According to some experts, the 24 solar terms were used for the first time in books during the Western Han Dynasty, __________ the Start of Spring was set as the Spring Festival.

A．where

B．when

C．that

D．which

2 . On the eve of the Spring Festival, I usually stay up until midnight, ________I can set off the firecrackers and fireworks.

A．which

B．when

C．where

D．who

3 . The picture often reminds me of the happy hours, ________ I was playing happily with my friends.

A．how

B．that

C．when

D．where