当遇到巨大声响时，为保护鼓膜，应该
①迅速张口②迅速闭嘴③张口，同时双手堵耳④闭嘴，同时双手堵耳[ ]
A．①④
B．①③
C．②③
D．②④
答案：A
His mother knew he his time all the time, but she couldn't do anything.[ ]
A. is wasting
B. has wasted
C. was wasting
D. wastes
期货合约涨跌停板的确定主要取决于（）。
A.标的物市场价格波动频繁程度
B.标的物市场价格波动波幅大小
C.标的物交割月份
D.标的物交易时间
