1. A ladder leans up against a wall. If the ladder is not to slip, which one of the following must be true? a.friction between the ladder and wall must not be zero b.friction between the ladder and floor must not be zero c. both a and b d. either a orb e. neither a or b 2. net force =0, net torque = 0 3. i think it should be b. Can someone concur or correct me?