why can't black capture c5?
@rtgfoi In most of draughts variants you can't jump over captured piece (draughtsman or king) twice, and under this rule in real life tournaments you must remove all captured pieces only after the capturing move is finished. This rule is called 'Turkish strike' rule.
In your case, black king can't take draughtsman b4 two times.
@kalnap thank you for letting me know