A small ball moving rightward with speed $v_0$ on a long horizontal track meets a smooth bend that connects to a straight ramp inclined at angle $\theta$ above the horizontal. The ramp rises to a point $B$ at height $h$ above the flat section, where the track abruptly ends. The ball rolls without slipping along the track and behaves as a point projectile after it leaves the track at $B$. The launch speed is large enough that the ball reaches $B$ with positive speed and is thrown into the air. Which of the following best describes the horizontal velocity $v_x$ of the ball as a function of time, from its motion on the flat section through the airborne phase?