关于跟骨侧位叙述错误的是（）

A.被检侧足部外踝紧贴暗盒并置于胶片中心

B.距骨下关节面呈切线位显示，关节间隙清晰显示

C.照片显示包括踝关节

D.跟骨纹理显示清晰

E.中心线对准内踝

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.

（72）是（）

A.length

B.pair

C.size

D.space