我们记得，这是个以单位速度旋转的向量场。
Remember that was the vector field that looked like a rotation at the unit speed.
这是一个绕原点逆时针旋转的向量场。
It's a vector field that just rotates around the origin counterclockwise.
这是一个向量场，其中旋转轨道是，以z轴为圆心的圆周，并且这个向量场与每个圆相切。
That is a vector field in which the trajectories are going to be circles centered in the z-axis and our vector field is just going to be tangent to each of these circles.
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