Sources 1 and 2 emit lights of different wavelengths whereas sources 3 and 4 emit light of different intensities.
The coherence

Options

A. can be obtained by using sources 1 and 2
B. can be obtained by any of these sources
C. cannot be obtained by any of these sources
D. since contrast suffers when sources 3 and 4 are used so coherence cannot be obtained by using sources 3 and 4

Answer

b

Explanation

Different wavelengths would correspond to different frequencies. Lights of different intensities can give coherence even if contrast is poor