Which question is most useful while choosing a business idea?

Correct answer: Does it solve a real need or problem?

A strong business idea should respond to a genuine customer need or problem and create useful value. Asking this question encourages research into demand, feasibility, and the benefit offered before resources are committed. Profit without effort, a business without customers, and permanent zero cost are unrealistic assumptions. Therefore, option A is the most useful and evidence-oriented question.