不同的地区和国家，地理位置不同，自然环境与历史文化前景千差万别，社会经济发展的水平也各不相同。据此回答题。

小题1:欧洲西部畜牧业发达的主要因素是（ ）

A．欧洲人喜吃牛羊肉

B．高原为主的地形

C．河网稠密

D．终年温和湿润的气候小题2:有着“民族大熔炉”特点的国家是（  ）

A．

B．

C．

D．

In a public-key cryptosystem, (71) encrypted with the public key can only be deciphered with the private key from the same (72) . Conversely, (71) encrypted with the private key can be decrypted only with the public key. Users can make their public keys (73) available or place them at a key distribution center or others to access. However, the private key must be (74) safe. In public-key systems there’s no (75) to find a safe channel for communicating a shared secret key.

（71）是（）

A.binarytext

B.hypertext

C.plaintext

D.supertext