The idiom "to jump on the bandwagon" means:

Explanation

The correct answer is Option B: 'To support something because it is popular.' This idiom suggests that individuals often adopt beliefs or actions based on their popularity rather than their own convictions. In contrast, Option A is incorrect because it suggests opposition to popular opinion, which is the opposite of jumping on the bandwagon. Option C is incorrect as it relates to quitting rather than supporting something. Finally, Option D is incorrect because it implies activism, which does not capture the essence of the idiom. In summary, the idiom reflects a tendency to go along with what is widely accepted or trendy.