A. carrier frequency times the ratio of maximum velocity of a transmitter divided by propagation velocity

B. carrier frequency times the ratio of minimum velocity of a transmitter divided by propagation velocity

C. carrier frequency times the ratio of propagation velocity divided by maximum velocity of a transmitter

D. carrier frequency times the ratio of propagation velocity divided by minimum velocity of a transmitter

I had been asked this question in a job interview.

The query is from Antenna Tradeoffs in division Technology Tradeoffs in Software Defined Radio of Cognitive Radio

To explain I would say: Doppler spread is given by carrier frequency times the ratio of maximum velocity of a transmitter divided by propagation velocity. Doppler spread is observed in the study of spatial coherence.