A soccer player kicks a ball with an initial velocity of 10 . meters per second at an angle of $30 .{ }^{\circ}$ above the horizontal. The magnitude of the horizontal component of the ball's initial velocity is
(A) $5.0 \mathrm{~m} / \mathrm{s}$
(B) $8.7 \mathrm{~m} / \mathrm{s}$
(C) $9.8 \mathrm{~m} / \mathrm{s}$
(D) $10 . \mathrm{m} / \mathrm{s}$