必须保持

1.On this superhighway drivers should keep to a speed of over 80 miles per hour.

这条高速公路上,驾驶员必须保持每小时80英里以上的速度。

2.A policeman has to keep on his toes all the time he's on duty.

警察执勤时必须时刻保持警覺。

3.Athletes have to train continuously to stay in peak condition.

运员必须不断训练才能保持最佳竞技状态。