The statement that best explains why your body continues to move forward when your foot stops is: An unbalanced force stops your foot but does not act on the rest of your body.
This explanation relates to Newton's First Law of Motion, which states that an object in motion will remain in motion unless acted upon by an external force. When you trip, the force applied to your foot (such as the ground) causes it to stop, but your body, due to inertia, tends to continue moving forward until another force acts on it (like gravity or the ground when you fall).