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.

已戒煙者的發(fā)病率與少量吸煙者相仿，但為不吸煙者的5倍。

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

1970年以來，農(nóng)村診所的數(shù)量比原來增加了1倍多。

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

各種抗生素的產(chǎn)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.

按目前的增長(zhǎng)速度，地球上的人口將在35年內(nèi)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.

大多數(shù)報(bào)告指出，此病的發(fā)病率比過去10%的發(fā)病率增加了數(shù)倍。

表示倍數(shù)增加時(shí)，常用介詞to和by，兩者含義完全不同，不可混淆。to 表示“增加到……”,by表示“增加了……”（即凈增加倍數(shù)）。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.

去年該廠產(chǎn)值為1972年的6倍。