OFFICIAL EXPLANATION
Preparing for a marathon, a well-balanced diet should be strictly followed by runners.A. Preparing for a marathon, a well-balanced diet should be strictly followed by runners
This sentence begins with a modifier: Preparing for a marathon. A modifier should be placed right next to the noun it describes. The only noun that this modifier can logically modify is runners, as it's hard to imagine a diet preparing for a marathon... However, the noun runners is quite far from the modifier that describes it.
What helps us identify this question as a Dangling Modifier question as well as identify the mistake is the following Stop Sign:
A modifier, characterized by all of the following:
1. Verb+ing or Verb in 3rd form
2. Separated from the rest of the sentence by a comma
3. Appears at the very beginning of the sentence
Whenever you see this Stop Sign, focus on the modifier: check whether the noun right after the modifier is indeed the noun that the modifier describes. If it isn't - you've found your mistake.B. Runners should strictly follow a well-balanced diet while preparing for a marathon
The original sentence creates a misplaced modifier error: Preparing for a marathon is a modifier, and should be placed right next to the noun it describes.
This answer choice corrects the original mistake by adding the connector "while", which turns "preparing for a marathon" into a time reference which can be placed anywhere without modifying any particular noun.C. Preparing for a marathon, a well-balanced diet should be followed by runners as strictly as possible
This answer choice repeats the original mistake. This sentence begins with a modifier: Preparing for a marathon. A modifier should be placed right next to the noun it describes. The only noun that this modifier can logically modify is runners, as it's hard to imagine a diet preparing for a marathon... However, the noun runners is quite far from the modifier that describes it.
What helps us identify this question as a Dangling Modifier question as well as identify the mistake is the following Stop Sign:
A modifier, characterized by all of the following:
1. Verb+ing or Verb in 3rd form
2. Separated from the rest of the sentence by a comma
3. Appears at the very beginning of the sentence
Whenever you see this Stop Sign, focus on the modifier: check whether the noun right after the modifier is indeed the noun that the modifier describes. If it isn't - you've found your mistake.D. Runners should strictly prepare and follow a well-balanced diet before a marathon
Although this answer choice corrects the originalDangling Modifier mistake and is grammatically correct, it changes the meaning of the original sentence. In the original sentence, the runners are preparing for a marathon. They are not necessarily preparing their diets.E. A diet that is well-balanced should be strictly followed by runners while they are preparing for a marathon
Although this answer choice corrects the original dangling Modifier mistake and is grammatically correct, stylistically it is not the most concise of the five answer choices. Changing the sentence from active to passive and the addition of the words that is and they are create redundancy.
Active (more concise): Runners should follow a diet.
Passive (less concise): A diet should be followed by runners.
There's another grammatically correct answer that is more concise than this one. Look for it!