The statement that best explains why your body continues to move forward when you trip is: "An unbalanced force stops your foot but does not act on the rest of your body."
This is consistent with Newton's First Law of Motion, which states that an object in motion will stay in motion at a constant velocity unless acted upon by a net external force. When your foot trips and stops, the rest of your body continues to move forward due to inertia until another force acts on it (like the ground when you fall).