The dirt pushing back is the 'resistance' force. It RESISTS your attempts to shovel it.
Gravitational energy is the potential energy associated with gravitational force. If an object falls from one point to another inside a gravitational field, the force of gravity will do positive work on the object and the gravitational potential.
Found this on cha-cha.com
Work=Force x Distance
2x25=50
The correct answer is C