1. [单选题]在Shell变量引用操作符可实现字符串替换其中()用来测试如果变量stra存在且不为空，则返回为word,否则返回为空串
A. ${stra:-word}
B. ${stra:=word}
C. ${stra:+word}
D. ${stra:?word}
2. [单选题]如何停止一台机器的telnet服务()
A. Put NONE in/etc/telnet.allow
B. Put a line&39;ALL:ALL&39;in/etc/hosts.deny
C. Comment the telnet entry in/etc/inittab
D. Comment the telnet entry in/etc/xinet.conf
