A protein called RB normally blocks cell cycle progression from G1 to S. Phosphorylation inactivates RB. Which of the following, related to RB and its function, might result in a cell turning cancerous?
(A)increase in RB levels
(B)loss of RB phosphorylation
(C)overproduction of kinases that phosphorylate RB
(D)inactivation of the DNA replication machinery in S