Final answer:
Option B: Increasing the coefficient of friction between the brick and the horizontal surface will increase the frictional force.
Step-by-step explanation:
To increase the frictional force on a brick sliding on a horizontal surface, we can consider a few factors. Among the options presented, increasing the coefficient of friction (b) between the brick and the surface will indeed increase friction. This is because the coefficient of friction is a measure of how much two surfaces resist sliding against each other. It is independent of both the surface area of contact and velocity of the brick - simplifying the frictional force to be primarily reliant on this coefficient and the normal force (the force perpendicular to the surface contact).
Option (a), decreasing the surface area of contact, does not affect the friction of sliding objects significantly because friction does not depend on contact area. Reducing the velocity of the brick (c) will not increase friction since kinetic friction is nearly independent of speed once the brick is in motion. Lastly, lubricating the surface (d) would actually reduce friction, as substances like oils are used to decrease the adhesive forces between the surfaces, leading to less resistance.