why does this sentence need the 'ke'?
Because there is a definite article ("het"). See here for more info.
kind is a het word ,usually het words doesnt take the additional e ,does it??
I cannot open the link, but I would like to know why the 'ke' is needed.
Ah, this one should work, I think: https://www.duolingo.com/comment/3888221
What's the difference between swak and swakke?
I understand you need the 'e' because het is before it but why 'zwakke' and not 'zwake'?