Perl 5, 42 bytes

41 bytes code + 1 for -p.

s//K Ks
K unKs/;s/K/known/g;$\=s/^/un/gmr

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Perl 5, 45 bytes

Tried to come up with an alternative, but couldn't make it shorter... Thought it was different enough to warrant adding anyway.

print"un"x/[3467]/,known,$_%2?"s
":$"for 0..7

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