Answer: Option C
An idiom is a phrase or expression that has a figurative meaning different from the literal meaning of the words. In this case, the phrase "broke down" is an idiom that means to stop working due to mechanical failure.
Here is an explanation of the possible options:

• Option A - met with an accident: This phrase means to have an accident and is not relevant to the situation described in the sentence.
• Option B - broke into pieces: This phrase means to break something into many small pieces and is not relevant to the situation described in the sentence.
• Option C - stopped due to mechanical failure: This phrase is the correct meaning of the idiom "broke down" in the sentence. It means that the car stopped working due to a mechanical problem.
• Option D - dashed against another vehicle: This phrase means to crash or collide with another vehicle and is not relevant to the situation described in the sentence.
• Option E - None of these: This option is incorrect as Option C - stopped due to mechanical failure is the correct answer.

In summary, the idiom "broke down" means to stop working due to mechanical failure. Therefore, Option C - stopped due to mechanical failure is the correct meaning of the idiom in the sentence "My car broke down on the way to college yesterday."