Which process(es) is/are involved in the turning of starch iodide paper blue-black by chlorine gas?

A.
chlorine attacks the starch to give the blue-black color
B.
chlorine attacks the iodide ion to give the blue-black color
C.
chlorine oxidizes the iodide ion to produce iodine which attacks the starch to give the blue-black color
D.
iodine attacks the starch to give the blue-black color

There is an explanation video available below.

The N.C.N.C sent a delegation to London in 1947 to protest against the