Final answer:
A strain mutant for the gene-encoding enzyme B would require a medium that supplements the missing nutrients it can't synthesize. The only suitable medium would be one containing both nutrients A and B, as it already can produce nutrient C. The correct option is B.
Step-by-step explanation:
A strain mutant for the gene-encoding enzyme B would be capable of growing on a medium where the nutrients it cannot synthesize are supplied. Since enzymes A, B, and C are all required for growth, a mutant strain lacking enzyme B would not be able to produce nutrient B on its own. Therefore, the only medium that it would be able to grow on would be the one that provides this missing nutrient, which is either nutrient B or a combination of nutrients that includes B.
In this scenario, the correct option would be:
- B. minimal medium supplemented with nutrients A and B
This is because the strain already has the ability to make nutrient C, but since it is mutant for the gene-encoding enzyme B, it requires both nutrient A (which it can't make due to the mutation) and nutrient B (to compensate for the lack of enzyme B) to be added exogenously for growth. Hence, B is the correct option.