JEE Main 2019 Physics question

A train moves towards a stationary observer with speed 34 m/s. The train sounds a whistle and its frequency registered by the observer is . If the speed of the train is reduced to 17 m/s, the frequency registered is . If speed of sound is 340 m/s, then the ratio is:

• (A)19/18Correct
• (B)20/19
• (C)21/20
• (D)18/17