Answer
B.
Work Step by Step
Proto-oncogenes are genes which normally turn on the cell cycle (B.), but, when mutated, leave it on constantly, leading to over production of cells and tumor formation. A. is wrong because there are two copies of each proto-oncogene per diploid genome, and C. can be eliminated because it is the opposite of B. D. is not true since proto-oncogenes act in a dominant fashion, meaning that only one copy needs to be mutated for cancer to form.