Around 120 years ago, Ebbinghaus began his study of memory. He(26) .on studying how quickly the human mind can remember (27) . One result of his research is known as the total time hypothesis( 假设 ), which simply means the amount you learn (28) on the time you spend trying to learn it . This can be taken as our first rule of learning. Although it is usually true that studying for four hours is better than studying for one, there is still the question of how we should use the four hours. For example, is it better to study for four hours (29) or to study for one hour a day for four days in a (30) ? The answer, as you may have (31) , is that it is better to spread out the study times. This (32) , through which we can learn more efficiently by dividing our practice time, is known as the distribution of (33) . Thus, our second rule of learning is this. It ’ s better to study fairly briefly but often. But we are not finished yet. We haven ’ t considered how we should study over very short periods of time. Let ’ s say you are trying to learn some new and rather difficult English vocabulary using(34) . Should you look at the same word in (35) or look at the word and then have some delay before you look at it again? The answer is it is better to space up the presentations of the word you are to learn.