导致石油开采业发展、石油化工产业和陆空交通工具发明的最主要原因是
A．远洋轮船的出现
B．飞机的出现
C．汽车的出现
D．内燃机的创制和使用生产
答案：D
22. I _____ my university professor in the supermarket near my house, which was out of my expectation.
A．came out
B．came across
C．came about
D．came along
重载的关系运算符和逻辑运算符的返回类型应当是_______。
