当乙炔在空气中的体积分数达到40%时，长期接触这种气体可以引起中毒，主要表现为（）。
A、肺水肿
B、中枢神经系统受伤
C、尘肺
参考答案：B
--- Did you telephone Uncle Sam our plan for the Christmas holidays on his farm?
--- Yes, he was happy about our arrival, and he eagerly asked when .
A．has we arrived
B．we had arrived
C．were we arriving
D．we were arriving
辅导协议签订后可随时解除。( )
