A should be correct. Seem to remember that is even written in the T&Cs of the vouchers, no change given. If you convert them to cash, you also only get 50% of them.
For those guessing C, why should you be asked to pay with 4 vouchers for something that barely costs the 3 of them?
On a side note, is it normal to get the comp as several vouchers, my recollection from last I got off loaded, I just got one for the full amount. But maybe I am wrong. Used it as part of a C ticket, so any way had to top up in cash.