The surface area doesn't depend on the unit you use to describe it,
but the number in the description does.
Definition: 1 cm = 10 mm
Square each side: (1 cm)² = (10 mm)²
(1)² · (cm)² = (10)² · (mm)²
1 cm² = 100 mm²
So if the area is 100 cm² but you want to describe it in mm² instead,
the number will become bigger.
Choice-C says this.