As we can see the figure
When a stunt motorcyclist is performing the stunt then as per force diagram we will have a its force of gravity or weight acting downwards along the surface of cylinder
The normal force due to vertical wall is towards the center of circle
and friction force is counter balancing the weight of motor cyclist
Now here we can see that the Normal force is towards the center of the circle
So correct answer will be
c. the normal force.