OG-44 没人理我，再顶！

44. Using a Doppler ultrasound device, fetal heartbeats can be detected by the twelfth week of pregnancy.
A.Using a Doppler ultrasound device, fetal heart-beats can be detected by the twelfth week of pregnancy.
B.Fetal heartbeats can be detected by the twelfth week of pregnancy, using a Doppler ultrasound device.
C.Detecting fetal heartbeats by the twelfth week of pregnancy, a physician can use a Doppler ultrasound device.
D.By the twelfth week of pregnancy, fetal heartbeats can be detected using a Doppler ultrasound device by a physician.
E.Using a Doppler ultrasound device, a physician can detect fetal heartbeats by the twelfth week of pregnancy.

關於c，og的解釋是choice c suggests that physicians can use a doppler ultrasound device after they detect fetal heartbeats.前面的部分Detecting fetal heartbeats by the twelfth week of pregnancy和主句之間有先後關係嗎？我不知道有這種説法，請NN指點！先谢过了。

当然是E

分词做状语时，可以表示时间、让步、原因、条件、伴随 、结果...

在本题的考点是：现在分词做时间状语&分词的逻辑主语。

"Using a Doppler ultrasound device, a physician can detect fetal heartbeats by the twelfth week of pregnancy" 相当于 "After using a Doppler ultrasound device, a physician can detect fetal heartbeats by the twelfth week of pregnancy"

我觉得"C.Detecting fetal heartbeats by the twelfth week of pregnancy, a physician can use a Doppler ultrasound device." 的错误在于用了现在分词做目的状语，应该改为不定式，To decet fetal......, aphysician can use...."

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

阴影部分可以看作是方式状语。

+ing状语从句除了表伴随外，通常还有方式、原因等隐含意义。或者说，作为伴随状语从句（包括独立主格），在纯语法中，可能只是表示同时发生。但是，在GMAT或者说实际的使用环境中，不应该将两个完全无关的状态/事件并行在一句话中表达，在一句话中的，必然有相关关系，不论是表方式还是暗示原因。

因此，OG对C没有强调句子的中心转移，而是强调了逻辑上的意思改变。换句话说，改变原意是一项大于且包含改变重心的过错。