uses more than one caterpillar. performs the investigation on a wet surface. uses earthworms instead of caterpillars. performs the investigation at the same time on four days.
I gave my students this multiple choice question: A student investigates the effect of temperature on the distance a caterpillar travels in one minute. The student performs the investigation at four different times of day using one caterpillar. This experiment could be improved if the student

Only one answer is correct among these 4 choices:
- uses more than one caterpillar.
- performs the investigation on a wet surface.
- uses earthworms instead of caterpillars.
- performs the investigation at the same time on four days.

Could you tell me which one is correct?

uses more than one caterpillar.