we'll never know?it endwe'll never know___ it end.填how 还是what 还是which?

we'll never know?it endwe'll never know___ it end.填how 还是what 还是which?
we'll never know?it end
we'll never know___ it end.填how 还是what 还是which?

we'll never know?it endwe'll never know___ it end.填how 还是what 还是which?
how：空里面填副词,只有how能作副词.

应该选how

we'll never know__how
_ it end

how 怎样
end没有写错吗？时态不对啊！