Click on the sentence that expresses the implied main idea. (1) A researcher at Johns Hopkins University has repeatedly done a simple experiment with two rats. (2) He holds one rat firmly in hand so that, no matter how much the rat struggles, he cannot escape. (3) The rat will finally give up. (4) The researcher then throws that unmoving rat into a tank of warm water, and the rat sinks, not swims. (5) He has learned" that there is nothing he can do, that there is no point in struggling. (6) The researcher then throws another rat into the water-one that doesn't "know" that his situation is hopeless and that he is therefore helpless. (7) This rat will swim to safety (8) A comparable experiment involving people has been conducted by Martin E. P. Seligman of the University of Pennsylvania. (9) Two groups of college students are put in rooms where they are blasted with noise turned up to almost intolerable levels. (10) In one room there is a button that turns off the noise. (11) The students quickly notice it, push it, and are rewarded with blissful silence. (12) In the other room, however, there is no turn-off button. (13) The students look for one, find nothing, and finally give up. (14) There is no way to escape the noise (except to leave the room before a previously agreed-upon time period has elapsed), so they simply endure the noise. (15) Later, the same two groups are put in two other rooms. (16) This time, both rooms contain a switch-off mechanism -though not a simple button this time and not as easy to find. (17) Nevertheless, the group that found the button the first time succeeds in finding the "off" switch the second time, too. (18) But the second group, already schooled in the hopelessness of their circumstances, doesn't even search; its members just sit it out again. a. Past failures can teach one to feel helpless and, as a result, to give up trying. b. Experiments have shown that rats are more helpless than people. c. Researchers at two schools have discovered shocking facts through their experiments with helplessness, d. Past failures are not an indication of future performance.​