Two vehicles,each moving with speed $u$ on the same horizontal straight road,are approaching each other. Wind blows along the road with velocity $w$. One of these vehicles blows a whistle of frequency $f_1$. An observer in the other vehicle hears the frequency of the whistle to be $f_2$. The speed of sound in still air is $V$. The correct statement$(s)$ is (are) :
$(A)$ If the wind blows from the observer to the source,$f_2 > f_1$.
$(B)$ If the wind blows from the source to the observer,$f_2 > f_1$.
$(C)$ If the wind blows from the observer to the source,$f_2 < f_1$.
$(D)$ If the wind blows from the source to the observer,$f_2 < f_1$.

• A
  $(A, C)$
• B
  $(A, B)$
• C
  $(B, D)$
• D
  $(C, D)$