Read this excerpt from the time traveller by h. g. wells and then answer the question that follows: "now i want you clearly to understand that this lever, being pressed over, sends the machine gliding into the future, and this other reverses the motion. i am going to press the lever, and off the machine will go. it will vanish, pass into future time, and disappear. have a good look at the thing. look at the table too, and satisfy yourselves there is no trickery. i don't want to waste this model, and then be told i'm a quack." there was a minute's pause perhaps. the psychologist seemed about to speak to me, but changed his mind. then the time traveller put forth his finger towards the lever. he sent forth the model time machine on its interminable voyage. we all saw the lever turn. i am absolutely certain there was no trickery. there was a breath of wind, and the lamp flame jumped. one of the candles on the mantel was blown out, and the little machine suddenly swung round, became indistinct, was seen as a ghost; and it was gone—vanished! which of the following is an example of theme in this excerpt? time travel friends are enemies. seeing is believing. machinery

Whether or not a given study has the possibility of causing harm to participants:

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.

Why is mary salter ainsworth a central figure in psychology?