[单选题]
A ball is thrown with a bz6;6lr , t8dykne9f vveltu3wy rhjxsjf, o)xw,qjf3w5(o 0) 5focity of 20 m/s at an angle of $60^{\circ}$ above the horizontal. What is the horizontal component of its instantaneous velocity at the exact top of its trajectory?
