对于平均时间对动态范围的影响：平均时间越长，测试精度越高。
参考答案：对
— Excuse me, could you tell me ______?
— Sorry, sir. I wasn't there at that time. [ ]
A. how did the accident happen
B. how the accident happened
C. how does the accident happen
D. how the accident happens
指挥旗的旗杆长度应为（）cm
A、400；
B、450；
C、500；
D、550
