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.

（73）是（）

A.free

B.freely

C.locally

D.partly

自动重合闸只适用于（）线路，而不用适用于电缆线路。

A、架空

B、动力

C、控制

D、照明