将6，7，8，9这四个数分别填入下面的算式，使左边的和最大，右边的和最小．

根据句意和提示写出单词，完成句子。
（1）We should brush our____  (牙齿) after each meal.
（2）On his mother's____ (四十) birthday, he gave her a card and some flowers.
（3）Does your father like ____  (看) newspapers?
（4）You may____ (借) the book for two weeks.
（5）Now mankind is exploring those ____  (未知的)outer space in many ways.

地球自转的方向是____（北极上空往下看是____针），自转一周的时间约为____，也就是____．