液体在静止后，其（）在各种力的作用下，自然形成了（）。这个特性称为液体的（）。
参考答案：上部表面；自由水平表面；表面特性
I wonder ____ made your English teacher so angry in her class this morning.
A what was it that B how was it that C what it was that D how it was that
河流中的泥沙受水流挟带而运动，水流的携沙能力与流速是（）关系。
