An iron block of sides $50\; cm \times 8 \; cm \times 15\; cm $ has to be pushed along the floor. The force required will be minimum when the surface in contact with ground is :

Question

( A ) $5\; cm \times 15 \; cm$ surface
( B ) $8 \; cm \times 5 \; cm$ surface
( C ) $8\; cm \times 15 \; cm$ surface
( D ) force is same for all surface