Some cattle were given bovine growth hormone (BGH) to see if they would produce more meat. The animals were studied over a period of two years. Animals in Group A were injected with BGH. What was the independent variable in the experiment?
(EXPLAIN HOW YOU GOT THAT LETTER CHOICE)
A. The amount of BGH that each group received
B. The amount of meat produced
C. The size of the cow
D. The time the cows were observed.