Test Tube	Substrate Added	Enzyme Added	Temperature ( ${ }^{\circ} C$ )
1	Yes	No	10
2	Yes	Yes	10
3	Yes	No	20
4	Yes	Yes	20
5	Yes	No	30
6	Yes	Yes	30
7	Yes	No	40
8	Yes	Yes	40

Which test tubes are controls in the experiment?

ATest tubes 1 and 2 only

BTest tubes 5 and 6 only

CTest tubes 1, 3, 5, and 7

DTest tubes 2, 4, 6, and 8