油品蒸气与空气混合物发生爆炸属于（）。
A.物理性爆炸
B.化学性爆炸
C.物理化学性爆炸
D.有可能是物理性爆炸，也有可能是化学性爆炸
参考答案：B
_______, Jack couldn’t get the door open. He had to dial 119.
A．As he might try
B．Try as he might
C．As might he try
D．Might as he try
－When should I hand in my paper? －It after class.
A．must be handed in
B．is handed in
C．was handed in
D．will hand in
