B

    As we all know，having a great memory is important．It can help you succeed in school，in your job，and in life．It also helps you learn faster and better．We all know that fast learner's are always in demand．If you have a great memory, I'm sure you can succeed more easily．

    If you are willing to make a few changes in your life．you should improve your memory first．My plan is to explain every skill that can help you improve your memory．

    You can not only learn memory skills on this website，but also learn how to improve your memory through diet，exercise，sleep and other ways．

    I think that memory improvement can be achieved (实现)in two ways：improving the health of your brain and using memory skills．Many people think they may be difficult．In fact, they are easier to do than you might think，but you have to work hard by yourself.

    Memory improvement needs time and effort on your part．You cannot improve your memory if you do not work on it．Of course，I believe that a more powerful brain is well worth the effort!

    Here are a few of the great memory improvement tips．I will give you some tips in the following part．

1926年美国人____制造了第一枚现代火箭。当运载火箭的速度达到____时，它就能挣脱地球的引力围绕地球运转。