As Jack pulls his wagon down the street it moves faster and faster. Jill, sitting a few meters ahead on the sidewalk, wants to slow Jack's wagon down so that it travels with a constant speed. How can Jill accomplish her goal? A) Push the wagon with a force greater than Jack. B) Push Jack away from the wagon so that he is no longer pulling it. C) Pull on the wagon in the opposite direction with twice Jack's force. D) Push the wagon in the opposite direction at a constant force less than Jack.