气焊作业前应对哪些设施进行检查？
参考答案：检查焊割炬、胶管、氧气瓶、乙炔瓶、减压器、压力表等工具。
John, who is seventeen this year, usually eats ____ his father does. No wonder he is growing taller. [ ]
A. twice more than as much as
B. more than twice as much as
C. twice as much as more than
D. twice as more than much as
若干进程之间相互合作，共同完成一项任务，进程的这种协同工作关系称为( )。
A．异步
B．同步
C．并发
D．互斥
