Which option accurately describes an unbalanced force?

a. a 2-n force presses down on the cement block at the same time as a 1.5-n force presses up on the cement block.

b. the force of a house pressing down on its foundation of cement blocks is 3,000 n.

c. each cement block supports a 2-n force, but when the foundation is built in a staggered pattern, it can support 2,000 n.

d. three rows of cement blocks form a foundation for a house, and the house rests on this foundation.