by表示时间和单位的用法

by表示时间和单位的用法

■ by表示时间的用法

表示时间，指“最迟在……之前”“到……的时候已经”，此时要注意它所连用的时态。如：

He was very tired by the evening. 他到晚上已经很累了。

He has read about 40 pages of the book by now. 现在这本书他已读了大约40页。

We will have finished the work by next month. 到下个月我们就会干完了这工作。

By the time the doctor arrived the patient had died. 在医生到达时，病人已经死了。

另外，表示时间时，它还可表示“在……期间”，通常连用的名词是 day, night, moonlight, daylight等，注意名词前通常不用冠词。如：

Cats sleep by day and hunt by night. 猫白天睡觉，夜里捉老鼠。

Do you like to swim by moonlight? 你喜欢在月光下游泳吗?

■ by表示单位的用法

表示单位，意为“以……计”，其后通常接表示计量单位的单数名词，且名词前要用定冠词。如：

They are paid by the hour (by the month). 他们所得报酬按小时（月）计。

Milk is sold by the pint, butter by the pound, and eggs by the dozen. 牛奶按品脱卖，黄油论磅卖，蛋类论打卖。

有时也接抽象名词，此时通常不用冠词。如：

Bananas are usually sold by weight. 香蕉通常按重量卖。