大气污染源调查的方法一般有()。
A.现场实测法
B.物料衡算法
C.遥感法
D.经验估计法
参考答案:A, B, D
Nacre is a substance that is ______
A.mechanically manufactured
B.the result of laboratory testing
C.organically secreted by the mollusk
D.present in the chemical composition of freshwater pounds
粘性流体总水头线沿程的变化是:()
A.沿程下降
B.沿程上升
C.保持水平
D.前三种情况都有可能