小儿肠套叠，可采用空气灌肠复位，但其时间限制在起病后不超过()
A．6小时
B．8小时
C．12小时
D．24小时
E．48小时
参考答案：E
These shoes look very good. I wonder ____. [ ]
A. how much cost they are
B. how much do they cost
C. how much they cost
D. how much are they cost
带速更高或特别重要的场合，带轮常选用的材料是（）
A.铸钢
B.铸铁
C.铝合金
D.工程塑料
