The weight of the moon is only about of that of the earth.A. one eightyB. one of eighty C

问题补充：

The weight of the moon is only about of that of the earth.

A. one eighty

B. one of eighty

C. one the eightieth

D. one eightieth

答案：

A. one eighty

B. one of eighty

C. one the eightieth

(答案→)D. one eightieth

解析：考查分数的表达：句意：月球的重量只是地球的重量的80分之一。分数的表达是：分子（基数词）+分母（序数词），如果分子是大于一，分母用复数，选D。