有关左心室射血分数（EF）的描述，错误的是（）。

A.射血分数用来反映左心室的泵血功能

B.EF=SV／EDV

C.EF静息状态下不小于50%

D.EF=SV／CO

E.左室射血分数可受心脏后负荷的影响，但它仍是反映左心室收缩功能的可靠指标

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.

A. free B. freelyC. locally D. partly