2.5÷a□a(a≠0),□里应填[ ]
A.大于
B.小于
C.无法确定
答案:C
You'd better book a ticket ______ if you want to see the 2012 London Olympic Games. [ ]
A. in advance
B. in charge
C. in trouble
D. in order
为了更好显示地甲状腺肿物内彩色血流信号并测速,最理想的探头频率是:
A.2MHz~2.5MHz
B.2.MHz~3MHz
C.3MHz~3.5MHz
D.5MHz~MHz
E.以上都不是