判断一辆汽车过去是否喷漆，一般采用打磨法。
参考答案：对
减压阀的基本作用原理是靠阀内流道对水流的局部阻力降低水压。
That man over there must be our English teacher, ?[ ]
A. needn't he
B. mustn't he
C. doesn't he
D. isn't he
