岩体的各向异性怎样产生的？
参考答案：
主要是层理、节理、片理面、片麻理面等的存在，造成平行结构面方向和垂直结构面方向物理力学性质不同。
我国南极考察站中，无极昼极夜现象的是：
A．昆仑站
B．长城站
C．中山站
D．无法判断
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 (71) ciphers, information is encrypted with (72) both the sender and receiver hold privately. Public-key encryption methods are called (73) ciphers, (74) created for each user, encryption key and deception key are (75)
A．synchronous
B．Asynchronous
C．symmetric
D．asymmetric
