If forces acting on an object are unbalanced, the object could experience a change direction, or both

The correct answer is

speed

In fact, Newton's second law states that:

where the term on the left is the resultant of the forces acting on an object, m is the object's mass, and a is its acceleration. We see from the formula that if forces acting on an object are unbalanced, this will result in a non-zero acceleration of the object.

A non-zero acceleration means a change in velocity of the object: since velocity is a vector, it consists of a magnitude (the speed) and a direction. Therefore, a non-zero acceleration means a change in either the speed of the object, or in its direction.

coil wire, increase current, put iron inside the coil

the answer would be c