"The frogs that did not get the extra protein" represents the control group.
Option: A
Step-by-step explanation:
A category that does not obtain treatment from researchers in an experiment or study, and is instead used as a benchmark to assess how the other subjects studied do, is understood as control group.
Jamal is performing such experiment to test the muscle strength in frogs by providing additional proteins to 20 frogs while excluding other 20 from such source, in order to see the difference on their respective jump.
This is done because frog legs are rich in protein, vitamin A, omega-3 fatty acids, and potassium. As providing more protein can increase their muscle strength, which directly motivate them to jump high from those who did not consumed additional protein.