Which of the following statements is wrong about curl? A: The curl of a vector field is a scalar and a function of the spatial coordinate points. B: At a certain point M in the field,[img=84x28]1803b721c59068a.png[/img] means that the vector line of this point is spinning. C: At a certain point M in the field,[img=84x26]1803b721cd97fe6.png[/img] means that the vector line of this point is spinless. D: Curl have the dimension of circumferential area density.