Which hydrogen in compound (E) is easily replaceable during bromination reaction in presence of light ?
`underset("(E)")(CH_(underset(delta)(3))-CH_(underset(gamma)(2))-underset(beta)(CH)=underset(alpha)(CH_(2)))`
A. `alpha` -hydrogen
B. `gamma`-hydrogen
C. `beta`-hydrogen
D. `delta`-hydrogen