A mercury barometer reads $75 \mathrm{~cm}$. If the tube be inclined by $60^{\circ}$ from vertical, the length of mercury in the tube will be
(A) $37.5 \mathrm{~cm}$
(B) $150 \mathrm{~cm}$
(C) $\frac{75 \sqrt{3}}{2} \mathrm{~cm}$
(D) $100 \mathrm{~cm}$