检查氧气系统，两个压力表的差不得（）
A、大于50PSI
B、大于200PSI
C、大于500PSI
参考答案：B
_______ she was invited to the ball made her very happy.
A．Whether
B．That
C．Because
D．What
结肠癌病灶穿透肠壁，无淋巴结转移的是（）。
A.DukesA1期
B.DukesA2期
C.DukesB期
D.DukesC期
E.DukesD期
