Using a Doppler ultrasound device, fetal heartbeats can be detected by

Hi,

Take a look at these sentences:

1. Wearing a designer outfit, Mary went to the party.

2. Arranging the books on the shelf, grandfather narrated a fairy tale to the children gathered in the room.

3. John decided to take his car to a garage, detecting problems in the engine.

4. The callers can avoid toll on home phones, using their mobile phones to make long-distance calls on weekends.

In all the above sentences, the verb-ing, either in the beginning of the IC or after the IC, modifies the doer of the action in the IC. If we use only the verb form of these verb-ing modifiers and rewrite every sentence in two simple sentences, then they would read:

1. Mary wore a designer outfit. She went to the party.

2. Grandfather arranged the books in the shelf. He narrated a fairy tale to the children.

3. John detected problems in the engine. He decided to take his car to a garage.

4. The callers can use their mobile phones to make long-distance calls on weekends. This way they can avoid toll charges on their home phones.

In a nutshell, the action shown through the verb-ing is performed by the doer of the IC. So we need a doer for that action denoted by the verb-ing.

Now let’s take the OG question answer choice B:
Fetal heartbeats can be detected by the twelfth week of pregnancy, using a Doppler ultrasound device.

Now let’s see if the action denoted by the verb-ing modifier in this sentence can be attributed to the subject of the IC or not.

Fetal heartbeats can use a Doppler ultrasound device. Fetal heartbeats can be detected this way. Does the first sentence even make sense? Obviously no. So the verb denoted by the verb-ing cannot be attributed to the subject of the IC we need a doer of that action. Hence this answer choice is incorrect.

Now let us take a look at the correct answer choice:
Using a Doppler ultrasound device, a physician can detect fetal heartbeats by the twelfth week of pregnancy.

Now let us repeat the same exercise:
A physician can use a Doppler ultrasound device. He can thus detect fetal heartbeats by the twelfth week of pregnancy.
Makes all the sense, right?

Hope this helps.
Shraddha