[单选题]
A ball is thrown with a vel arge*g4 mi 9koc2e8,gocity of 20 m/s at9wr-ehak6 dm + ey+bv -l7 m4kl6vrz+f an angle of $60^{\circ}$ above the horizontal. What is the horizontal component of its instantaneous velocity at the exact top of its trajectory?
