汽车由静止开始做匀加速直线运动，速度达到v₀的过程中的平均速度为v₁，若汽车由静止开始以额定功率行驶，速度达到v₀的过程中的平均速度为v₂，且两次历时相同，则（　　）

A．v₁＞v₂

B．v₁＜v₂

C．v₁=v₂

D．条件不足，无法判断

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．keep

B．keeped

C．keeping

D．kept