Pls answer if u know the answer ^w^ thx! Friction .

A) is always and unwanted force

B) works in the opposite direction of motion

C) causes machines to work 100 percent efficiently

D) can be increased using lubricants, like oil

Calculate the first and second velocities of the car with four washers attached to the pulley, using the formulas v1 = 0.25 m / t1 , and v2 = 0.25 m / (t2 – t1) where t1 and t2 are the average times the car took to reach the 0.25 and the 0.50 meter marks. record these velocities, to two decimal places, in table e.