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(D) When there is no wind,the sound waves travel in straight lines radially outward from the point source.When a horizontal wind blows towards the lef

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(D) When there is no wind,the sound waves travel in straight lines radially outward from the point source.When a horizontal wind blows towards the left with a uniform velocity $v_w$,the effective velocity of the sound wave at any point is the vector sum of the velocity of sound in still air $(v_s)$ and the velocity of the wind $(v_w)$.If the sound wave travels in the direction of the wind (towards the left),its effective velocity increases,and if it travels against the wind (towards the right),its effective velocity decreases.This change in velocity causes the wavefronts to bend. According to Huygens' principle,the rays (which are perpendicular to the wavefronts) will bend in the direction of the wind.Specifically,the rays will bend towards the left because the wind carries the sound waves along with it,effectively 'pushing' the sound rays in the direction of the wind.Looking at the options,option $D$ shows the rays bending towards the left,which correctly represents the effect of a constant horizontal wind blowing towards the left.

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