Which of the following statements best explains the fact that there was no discernable difference between the groups on day 1?
a. beta carotene had been absorbed by the body in sufficient quantities, but vitamin a was not detected in the body.
b. beta carotene was excreted from the body before it could produce vitamin a.
c. beta carotene had not yet been absorbed by the body in sufficient quantities to influence the amount of vitamin a being produced.
d. beta carotene was consumed by the body in a quantity that was insufficient to produce vitamin a.