Askydiver's parachute fails to deploy. after some struggle, his reserve chute deploys in time to save his life. however, his landing is harder than normal and he feels his knee slightly hyperextend. he shakes it off and goes about his normal routine. later that day he begins experiencing knee pain. two days later he notices that his knee "pops" when he crouches and soon discovers he has dislocated his femur on the knee. what muscle was likely injured initially?

It is widely assumed that people need to engage in intellectual activities such as solving crossword puzzles or mathematics problems in order to maintain mental sharpness as they age. in fact, however, simply talking to other people—that is, participating in social interaction, which engages many mental and perceptual skills—suffices. evidence to this effect comes from a study showing that the more social contact people report, the better their mental skills. which of the following, if true, most seriously weakens the force of the evidence cited? (a) as people grow older, they are often advised to keep exercising their physical and mental capacities in order to maintain or improve them. (b) many medical conditions and treatments that adversely affect a person's mental sharpness also tend to increase that person's social isolation. (c) many people are proficient both in social interactions and in solving mathematical problems. (d) the study did not itself collect data but analyzed data bearing on the issue from prior studies. (e) the tasks evaluating mental sharpness for which data were compiled by the study were more akin to mathematics problems than to conversation.