短文填空在下面短文的空白处填上一个适当的词（该词首字母已给出），将完整答案写在下边相
应题号横线上。
If you don't use your arms or your legs for some time, they will become weak; when you start using
them again, they will gradually (逐渐地) become stronger again. Everybody knows this. Yet many people
do not seem to know that it is the s 1 with memory. When someone says that he has a good memory,
he really means that he d 2 give it enough chance to become stronger.
If a friend says that his arms and legs are weak, we k 3 that it is his own fault. But if he tells us that
he has a poor memory, many of us think that his p 4 are to blame, and f 5 of us know that it is just
his own fault.
Have you e 6 found some people can't read or write but they usually have b 7 memories? This is
b 8 they cannot read or write and they h 9 to remember things; they cannot write them down in
a little notebook. They must remember dates, names, songs and stories; so their memory is the whole time
being exercised.
So if you want a good memory, l 10 from these people: practise remembering.
1．________ 2．________ 3．________ 4．________ 5．________
6．________ 7．________ 8．________ 9．________ 10．________
,如图11(a)所示,一列横波沿该直线向右传播,
时到达质点1,质点1开始向下运动,经过时间
第一次出现如图11(b)所示的波形.则该波的周期为 ,波速为 。 