After a constant current I is applied to the ring, the ampere force on the ring is BIL, and the vertical component is hyperbolic θ.

A, b, c, according to Newton's second law, hyperbolic θ-mg=ma, then the acceleration in the ring direction is a = hyperbolic θm-g,

Then, in the vertical direction, when the current is not removed, the ring will move in a straight line at a uniform speed. After time t, the speed will reach the maximum, which is obtained by v=at:

v=BILcosθmt-gt，

Substituting the data, the result is: v =12× 2-10× 2 = 4m/s; So, B is wrong and C is right;

In time t, the rising height H= 12at2, which is obtained by substituting the data: H= 12×2×22=4m, so a is wrong;

D. When the current acts on the ring, the current direction is clockwise, and the ampere force component points to the center of the circle, which tends to decrease. After removing the current, the induced current generated by cutting is counterclockwise, and the ampere force component deviates from the center of the circle and tends to expand, so item D is wrong.

So choose: C.