在派生式CAPP系统中利用分类编码进行零件分类成组的主要依据是（）。

A.零件材料

B.特征矩阵

C.典型工艺

D.零件种类

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