Several middle school students want to build 30 solar eclipse projectors for children at an elementary school to use. The projectors make it easy and safe for people to view a solar eclipse. One possible design of a student-constructed solar eclipse projector is shown below. Image courtesy of NASA

Which of the following would be the most reasonable criterion the students should consider before building the projectors?
A.
It should be small enough to fit in a school backpack.
B.
It should be made of heavy enough materials so that it cannot easily be moved.
C.
It should be durable enough so that if it is dropped, it will not break.
D.
It should be made mostly of metal materials.