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)

AThe amount of BGH that each group received

BThe amount of meat produced

CThe size of the cow

DThe time the cows were observed.