要实现对Java代码的数字签名，对于代码的提供者要经过的4个步骤的正确顺序是（ ）。 ①创建JAR文件 ②创建密钥 ③对JAR文件进行数字签名 ④输出公钥证书
A．①③②④
B．①②③④
C．②①③④
D．①③②④
参考答案：B
解析：在Java2中支持数字签名技术。使得Java的安全控制可以针对外界的具体用户进行，从而提高了访问控制的粒度。外界用户首先对Java代码进行数字签名，运行该代码的本机Java运行系统可以通过对代码数字签名的验证，决定是否授予该代码相应的权限。对Java代码进行数字签名时，用的就是题目中的4个步骤。
任务型阅读 There are many things you can do to improve your memory(记忆力). Among them are many kinds of useful ways are well as taking special care of your health. It is important that you make yourself excited to make your memory more active. You can do this by doing some new activities and by changing your daily habits（习惯）. Learning a new skill helps your brain（大脑）to develop. When trying to remember something, you should pay special attention to the most important things about it .Do not allow other thoughts to enter your mind because this will reduce your chances of making right memories. An excellent way to help memory is to connect information with pictures. Try to see the pictures in your mind. Taking notes and keeping a diary will also be helpful. Healthy food and plenty of vitamins are necessary for your memory to work well. Drinking a lot of water also helps keep your memory. You must allow your brain to have enough sleep and rest. When you are asleep, your brain stores memory. Not enough sleep can cause problems with storing information .And being tired will also stop you from being able to think clearly and well. In order to keep your mind on your work, you must be free from worry. Generally keeping fit and normal health checks are both important as well-not just for improving your memory.
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