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.
Choice A presents a dangling modifier. The phrase beginning the sentence has no noun that it can logically modify and hence cannot fit anywhere in the sentence and make sense. Coming first, it modifies heartbeats, the nearest free noun in the main clause; that is, choice A says that the heartbeats are using the Doppler ultrasound device. Choice B contains the same main clause and dangling modifier, now at the end. Contrary to intent, the wording in choice C suggests that physicians can use a Doppler ultrasound device after they detect fetal heartbeats. In choice D the phrase using ... device should follow physician, the noun it modifies. Choice E is best.
我觉得文中对b 的解释不很充分，因为介词短语放在句尾其逻辑主语不一定要和主句主语一致，请大虾们指教。
