为了使数据电子信息达到“书面形式”保存或提交的法律要求，《电子商务示范法》规定界定了

下列命题中，条件p是结论q的充要条件的是（　　）

A．p：a=0，q：ab=0

B．p：a=b，q：（a-b）²=0

C．p：|a|=1，q：a=1

D．p：a=b，q：|a|=|b|

从迁移的观点看，“举一反三”属于( )

A．正迁移

B．负迁移

C．顺向迁移

D．逆向迁移

芝加哥商业交易所是美国最大的交易中长期国债期货的交易所。（）

In the following essay, each blank has four choices. Choose the most suitable one from the four choices and write down in the answer sheet. There are two types of key technology: private key and public key. Private-key encryption methods are called (71) ciphers, information is encrypted with (72) both the sender and receiver hold privately. Public-key encryption methods are called (73) ciphers, (74) created for each user, encryption key and decryption key are (75)

A．a key

B．two keys

C．three keys

D．four keys

发动机水冷却系中，冷却液的大小循环由（）控制。

A.风扇

B.节温器

C.分水管