Answer: option A - tumor-suppressor gene
Explanation:
A cancerous tissue is growing or spreading rapidly at a harmful rate. However, for a tissue to become cancerous, its "internal guard" usually known as a TUMOUR SUPPRESSOR GENE must have lost or reduced its function.
This loss of function occurs after mutation.
So, definitely, all affected individuals with cancerous tissues have mutated tumour suppressor genes unlike unaffected individuals.
Note that other options are WRONG, because none of them accurately distinguishes affected from unaffected individuals
