An observer located near these two sources of sound will hear
$\mathrm{f}_{2}=304$
$\therefore \mathrm{f}_{\mathrm{beat}}=\mathrm{f}_{2}-\mathrm{f}_{1}=304-300=4$
intensity ratio $=\frac{\mathrm{I}_{\max }}{\mathrm{I}_{\min }}=\frac{\mathrm{A}_{\max }^{2}}{\mathrm{A}_{\min }^{2}}=\frac{(4+5)^{2}}{(5-4)^{2}}=\frac{81}{1}$

$(A)$ $u=0.8 v$ and $f_5=f_0$
$(B)$ $u=0.8 v$ and $f_5=2 f_0$
$(C)$ $u=0.8 v$ and $f_5=0.5 f_0$
$(D)$ $u=0.5 v$ and $f_5=1.5 f_0$