What are you talking about
"Constant velocity" is another way of saying "zero acceleration".
I think so it ans wold be d.because if the source approaches the observer more and more wavefront will pass and it get squeezed.so wavelength decreases and frequency increases.
a)., b)., and c). are completely false.
There isn't a grain of truth among them.
In Physics, the technical definition of 'Work' is (force) times (distance).
