Why Will Gly-Met-Gly React with Cyanogen Bromide, but Gly-Cys-Gly Will

Why will Gly-Met-Gly react with cyanogen bromide, but Gly-Cys-Gly will not react with cyanogen bromide?
I. There would be a highly strained four-membered ring intermediate in the case of cysteine.
II. After the addition of the thiol of cysteine to the cyano-group, a stable thioether will be formed, which does not react any further.
III. After the addition of the thiol of cysteine to the bromo-cation, a stable thioether will be formed, which does not react any further.
IV. Cysteine cannot form a stable bromonium-ion intermediate.

A) I and II are correct
B) II and III are correct
C) I and III are correct
D) II and IV are correct