The correct answer is B.
An efficient solution solves the problem and does it in a quick, direct way without wasting any time. Efficiency is required to increase productivity in the labor market and to obtain better results.
This is to contrast effective solution which simply solves the problem without eliminating all the negative consequences. A solution may be obtained but some aspects of the problem still exist and a final solution is still looked for.
Efficiency is the state or quality of being efficient, or able to accomplish something with the least waste of time and effort; competency in performance.