The train _______ for two hours. [ ]
A. has left
B. left
C. has been away
D. has away
答案:C
味可分为单一味和()味两大类。
A、咸
B、化学
C、复合
D、物理
MB的载波频率是()
A.90MHZ
B.150MHZ
C.75MHZ
D.108MHZ