内浮顶油罐由于浮盘封住了油面，油气空间基本消除，所以油罐上不设（）和液压安全阀。
参考答案：机械呼吸阀
After ten years abroad, he still recognized his old colleagues ________ he set foot in China．
A．immediately
B．for the first time
C．while
D．moment
新疆的牧场属于
A．绿洲牧场
B．山地牧场
C．高寒牧场
D．温带草原牧场
