Answer:
Option b
Step-by-step explanation:
This is a nice and simple question!
Consider Newton's first law of motion. It states that an object at rest will remain at rest until acted upon by an unbalanced force. That being said the reverse is applicable as well, an object in motion will remain in motion unless acted upon by an unbalanced force.
Thus, according to Newton's first law of motion, an object at rest begins to move when an unbalanced force acts upon it.