[单选题]
A microphone is emitting a sound wave with a wavelell( s1q7 yztb3bp3xl+ h 2c+yength z:tbw-;2.uex )xab ryab g+y;of $15\,m$. Tom is $5\,m$ further away from the microphone than Mary. What is the phase difference of the sound wave, in radians, between them?
A. $\frac{π}{3}$
B. $\frac{2π}{3}$
C. $\frac{3π}{2}$
D. $3π$
