The Skinny Tires of a 10-Speed Racing Bicycle Require More

The skinny tires of a 10-speed racing bicycle require more air pressure than the fat tires on an equally massive mountain bike because

A) the racing bike moves faster.
B) the racing bike touches the ground over a smaller area than the bike with fat tires.
C) the area of contact of the racing bike's tires is greater than that of the bike with fat tires.
D) the racing bike exerts more force on the ground.