The answer is: D) evaluating the solution.
There is four stages of technological design:
1. identify a problem or need. In this example to create a paper airplane that would stay in the air for as long as possible.
2. design a solution. In this example, folding printer paper into four different planes.
3. implement, build, test the design.
4. determine if the solution met the need. In this example, the plane with the longest time as their best design.