10.
Since the food given to the fleas is the same for both groups then it is a constant in the experiment. Therefore, the answer is c.
11.
The heartbeat was the thing under study in the experiment and, according to the text, it may depends on the caffeine given to the fleas in group A, hence it is the dependent variable. Therefore, the answer is b.
12.
Since group B were given nothing else, this means that it will be the control group of the experiment. Therefore, the answer is d.