【问】 The specific gravity of a gas is the numerical ratio of its density with the density of astandard of reference，usually air.(TOEFL，72.1;74.3)

请分析上面的试题。

【答】 应记住科技英语里的一个固定词组the ratio of A to B(A与B的比率)。

The ratio of load to effort is termed the Mechanical Advantage.

载荷与作用力之比叫做机械效益。