Internet的域名结构是树状的，顶级域名不包括（）。
A.usa美国
B.com商业部门
C.edu教育
D.cn中国
参考答案：A
The experiment turned out to be ________, which wasn’t ______ they wanted.
A．a completely failing; as
B．a complete failure; what
C．completely failure; that
D．failed; 不填
