It is said that the gravity on Mars is only about of the gravity on earthA. three-eighth

问题补充：

It is said that the gravity on Mars is only about of the gravity on earth．

A. three-eighths

B. third-eighth

C. three-eighth

D. third-eighths

答案：

(答案→)A. three-eighths

B. third-eighth

C. three-eighth

D. third-eighths

解析：句意：据说火星上的重力是地球上重力的八分之三。分数的表达为分子用基数词，分母用序数词，当分子大于一时，分母的序数词用复数形式；故选A。