Question 4
Why are treads cut into the tyres of a motor car?
The right answer is the one marked above.
To increase the friction between the wheel and the road. Without enough friction the car can skid, and in muddy or sandy places the wheels spin on the spot instead of driving the car forward.
Cutting grooves actually removes rubber, so the contact area goes down, not up — and area would make no difference to the friction either way.