Three observers A, B and C measure the speed of light coming from a source to be `v_A,v_B` and `v_C`. The observer A moves towards the source and C moves away from the soure at the same speed. The observer B stays stationary. The surrounding space is vacuum everywhere.
A. `upsilon_A gt upsilon_B gt upsilon_C`
B. `upsilon_A lt upsilon_B lt upsilon_C`
C. `upsilon_A = upsilon_B = upsilon_C`
D. `upsilon_B = (1)/(2) (upslion_A + upsilon_c).`
