Friction always acts in a direction to the direction of motion.
a. equal
c. perpendicular
b. opposite

b.Opposite

Explanation:

Friction: It is that force which oppose the motion of any object.It is rubbing force.

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Friction always act in opposite direction of motion.

Friction force is applied to overcome the motion of object.

If equal friction force applied in opposite direction  to   applied force on the object due to which an object in motion  then the object will come to in rest.

When applied force is not equal to friction force then motion will not come in rest and continue move.

Hence, friction force always acts in a direction opposite to the direction of motion.

Answer : b.Opposite

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