Question

which of the following is an example of increasing friction intentionally?
waxing skis
oiling a squeaky door
adding grease to gears on a bike
throwing sand on an icy driveway

Explanation:

Waxing skis, oiling a door, and adding grease to bike gears reduce friction. Throwing sand on an icy driveway increases friction for better traction.

Answer:

Throwing sand on an icy driveway