A Free-Radical Addition of a Certain Compound X-Y to an Alkene

Multiple Choice

A free-radical addition of a certain compound X-Y to an alkene (R = alkyl) results in the conversion:
The first propagation step in the mechanism is
Therefore, what is the second propagation step in the mechanism?

A)

B)

C)
$$\mathrm { X } - \mathrm { Y } \longrightarrow \mathrm { Y } \cdot + \cdot \mathrm { X }$$
D) Both (b) and (c) are propagation steps.
E) Both (a) and (b) are propagation steps.