什么是恒定流动?什么是非恒定流动?
参考答案:
动平衡的流动,各点流速不随时间变化,由流速决定的压强、粘性力也不随时间变化,这种流动称之为恒定流动反之为非恒定流动。
Betty goes to learn how to play the violin every day _____ Saturday and Sunday.
She does housework on these days. [ ]
A. on
B. during
C. except
D. from
引用分析的局限