Answer:
If true, option (B) Many medical conditions and treatments that adversely affect a person's mental sharpness also tend to increase that person's social isolation most seriously weakens the force of the evidence cited.
Step-by-step explanation:
If true, the fact that medical conditions and treatments that affect a person's mental sharpness also increase that person's isolation could seriously weaken the evidence cited in this paragraph because it supports the idea that the more social contact a person has, the better mental skills that person presents. On this basis, if a mental condition or treatment curbs a person social life, then it would be ultimately hindering that person's mental skills.