8/2p5/8/8/8/8/k6P/4K3 w - - 0 1
Of course c5+.
It should matter to you, Alena, even if black can't force a draw with either move. Let me ask you this- if you were on the black side of this problem in a game, which move would you play at move 4? Surely you don't resign the position every time you know your opponent already has a winning position.
It's doesn't matter c6 or c5 for me because I know how to win this position.
Alena, why would black simply waste a tempo with 4. ....c6?
It's a winning position for white