现场拆装放射源过程中，造成辐射伤害的原因有哪些？
参考答案：
防护意识差；防护手段存在纰漏；人员未经培训；装卸不熟练；放射源泄漏；人员误照射等。
In the following essay, each blank has four choices. Choose the most suitable one from the four choices and write down in the answer sheet. There are two types of key technology: private key and public key. Private - key encryption methods are called (66) ciphers, information is encrypted with (67) both the sender and receiver hold privately. Public - key encryption methods are called (68) ciphers, (69) created for each user, encryption key and decryption key ale (70) .
A．synchronous
B．Asynchronous
C．symmetric
D．asymmetric
图中非正弦周期电流的频率为（）。
A．0.05kHz
B．0.1kHz
C．10kHz
D．20kH2
