12. The risk in exsmokers is similar to that in persons smoking small numbers of cigarettes, but is 5 times higher than in non-smokers.

已戒烟者的发病率与少量吸烟者相仿，但为不吸烟者的5倍。

13. The number of rural dispensaries has been more than doubled since 1970.

1970年以来，农村诊所的数量比原来增加了1倍多。

14. The production of various antibiotics has been increased six times as against 1960.

各种抗生素的产量比1960年增加了 5倍。

15. At the present rate of growth, the population of the Earth will double again in 35 years.

按目前的增长速度，地球上的人口将在35年内增加1倍。 

16. Most reports show the incidence of the disease has a severalfold increase over the previous incidence of 10 per cent.

大多数报告指出，此病的发病率比过去10%的发病率增加了数倍。

表示倍数增加时，常用介词to和by，两者含义完全不同，不可混淆。to 表示“增加到……”,by表示“增加了……”（即净增加倍数）。例如：

Neonatal death increased by more then two and a half times.

新生期死亡率增加了2.5倍多。

The factory increased its output value last year to 6 times the figure for 1972.

去年该厂产值为1972年的6倍。