A source of sound when stationary with respect to medium, emits sound of frequency f and wavelength  $\lambda$. Speed of sound with respect to medium is c. Speed of medium is $V_m$ {in case (c) and case (d) of column I}. The observer $O_1$  receives waves of frequency $f_1$  and wavelength  ${\lambda }_1$. The observer $O_2$ receives waves of frequency  $f_2$ and wavelength  ${\lambda }_2$. Speed of source with respect to ground is $v_s$ {in case (d) of column I}

Column-I		Column-II
A)	Medium at rest, source at rest, $O_1$ and $O_2$ moves as shown.	P)	${\lambda }_1<\lambda <{\lambda }_2$
B)	Medium at rest, $O_1,O_2$ at rest, source moves as shown.	Q)	$f_1<f<f_2$
C)	Medium moves as shown, source, $O_1$ and $O_2$ are at rest.	R)	${\lambda }_1=\lambda ={\lambda }_2$
D)	Medium moves, source moves, $O_1$ and $O_2$ are at rest. $(V_s>V_m)$	S)	${\lambda }_1>\lambda >{\lambda }_2$