1 . Please come back at four o'clock, ___________ your herbal medicine will be ready. (用适当的词填空)

3 . Since the late 1970s, _______daily smoking among high school seniors reached 30 percent, smoking rates among youth have declined. （用适当的词填空）

4 . Next month, ________ we will spend our winter holidays in our hometown, is approaching. (用适当的词填空)

5 . Between the two halves of the football game is a 15-minute break, __________ the audience can have a rest．

A．when

B．where

C．which

D．that

6 . The National Day falls on October 1st, ______ he was born. （用适当的单词填空）

7 . He will put off the picnic until May 1st, ______ he will be free. （用适当的单词填空）

8 . He will come to see me next July, ________ he won’t be so busy. (用适当的词填空)

9 . 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)

10 . Some language experts believe that 10,000 years ago, __________ the world had just five to ten million people, they spoke perhaps 12,000 languages between them. （根据句意填空）