请教doing和by doing的区别

numero

究竟什么时候用doing,什么时候用by doing呢?

试举下面一例:

22.   Using a Doppler ultrasound device, fetal heartbeats can be detected by the twelfth week of pregnancy.

(E) Using a Doppler ultrasound device, a physician can detect fetal heartbeats by the twelfth week of pregnancy.

答案是E,没问题,但我想问能否在using前面加上by?是否也是正确答案?

perpetual

好像意思上有点不同，请nn来讲讲罢~~~

qianrene

刚查的时候偶然看到，

黄皮OG47.: by providing such services as x, y, and z, and by staying with…., America Bank has become….加不加by都可以

hopelanxyn

以下是引用qianrene在2007-9-23 22:23:00的发言：
刚查的时候偶然看到，

黄皮OG47.: by providing such services as x, y, and z, and by staying with…., America Bank has become….加不加by都可以

我怎摸没有看到说加不加都可以的话???

[此贴子已经被作者于2007-12-12 4:15:11编辑过]

Lilac29

If you want to use "by" before "using", you have to put this phrase in the sentences like the following:

A physician can detect fetal heartbeats by using a Doppler ultrasound device by the twelfth week of pregnancy.

The phrase "using a Doppler ultrasound device" is a prepositinoal phrase that functions as modifier.  You cannot put "by" there, otherwise you cannot use comma and you have to put it to the end of sentences.

I think the error of this sentence is dangling modifier.