[填空题]
Each string on a viol2 -d q +yljv9)ykqi0nyy 5 5j2yha) -zyrbpoh0in is tuned to a frequency 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?
$f_{A}$ = $\mu_{A}$
$f_{B}$ = $\mu_{A}$
$f_{C}$ = $\mu_{A}$
