Students conducted an experiment to determine if convection currents are strong enough to move heavy objects. They used a fish tank and a toy boat that floats. Initially, they placed the boat in the tank and observed it for 10 minutes; it did not move. Next, they placed a hot plate under one side of the fish tank and turned it on. After observing for a half hour, they noted that the boat had moved across the aquarium away from the heat.

What is a flaw in the experimental design of this experiment?

Options:
A. The toy boat should have enough weight to sink.
B. The hot plate should have been used in the first test.
C. The fish tank should have been filled with different liquids.
D. The amount of time should have been the same for both tests.