[填空题]
Each string on a violin is tuned to a frkn+of4jt+n blttprk3wlg ;7gm)4q 8 -pxng 2hvwj8: j5ct+2 d;1ywulequency 1$\frac{1}{2}$ times that of its neighbor. The four equal-length strings are to be placed under the same tension; what must be the mass per unit length of each string relative to that of the lowest string?
$f_{A}$ = $\mu_{A}$
$f_{B}$ = $\mu_{A}$
$f_{C}$ = $\mu_{A}$
