12. The enzyme in cholesterol biosynthesis subject to feedback inhibition is(A)ABCB4.(B)desaturase.(C)fatty acid synthase.(D)HMG CoA reductase.

13. How does inhibition of the Na+/K+ ATPase increase the force of heart muscle contraction?(A)It increases cytosolic Na+ and therefore decreases Ca2+ export.(B)It increases cytosolic K+ and therefore decreases Ca2+ export.(C)It decreases cytosolic Na+ and therefore decreases Ca2+ export.(D)It decreases cytosolic K+ and therefore decreases Ca2+ export.