不过，这个代替物却不能太高。在实验开始时，我原和小鸭子一样匍匐在草中，后来我逐渐换成坐的姿势。可是，等我一旦站起来试着带它们走，它们就不动了；A它们的小眼睛焦急地向四周探索，却不会朝上方看，没有多久，就像被弃的小鸭子一般，发出细细的尖叫，哭起来了。B因此，为了要它们跟着我，我不得不蹲着走，这自然颇不舒服。尤其糟的是，做母亲的水鸭子得时刻不停地叫唤，只要有半分钟的时间忘了“呱格格格、呱格格格”地唱着，小凫的颈子就拉长了，和小孩子拉长了脸一样。要是这时我不继续叫唤，它们就要尖声地哭了。好像只要我不出声，它们就以为我死了，或者以为我不再爱它们了。这真是值得大哭特哭的理由呢！

阅读理解

    If you put your history notes under your pillow (枕头) and sleep on them the night before an exam, will you do any better on the test? Most of us have hoped this might help. However, _______ can't go through the pillow into your brain. But that doesn't mean you can't learn while you sleep.  

    Scientists aren't exactly sure how it works, but they have discovered that the brain can learn things during sleeping hours.

    In one experiment(实验), researchers gave German speakers some Dutch words to learn. Then, they divided them into three groups. The researchers played Dutch words for people in Group 1 while they slept, without telling these German speakers what they were doing. The sound was low so it didn't wake them up, and only the newly introduced words were used.

    Another group listened to the same words while they were awake. The researchers found the people in Group 1 were better able to identify(确认) and translate the words later. This was true only for the words that were played while they slept. The third group listened to words while they walked. The walkers did not have the same success remembering the words as the sleeping group.

    The researchers later found that people had more slow-wave(慢波的) brain activity throughout the night. They said that more slow waves made people have better memory for the new words.