Answer:
(A) Protein x normally stimulates cell division.
Step-by-step explanation:
Protein who stimulates cell division are known as proto-oncogenes. If there is a mutation in proto-oncogene ,then this gene is converted into oncogene which causes cancer. Here protein x ( proto-oncogenes) normally stimulates cell division, if new mutation occurs in this gene, then this gene is converted into oncogene and resulted in the formation of cancer.