"Know that they exist."
Translation:Věz, že existují.
To je oříšek... "Vím, že existují" would translate to "I know they exist." Which is a completely different sentece.
However, I agree that "věz" is ridiculously formal and almost archaic. But - how else to translate it? I actually wonder that the contributors agreed to such an improbable Czech sentence... The best translation I can think of is an indirect expression: "Měj na paměti, že existují." More like "Beware that they exist." Or "Věř tomu, že existují = Believe that..."
As far as I am concerned, I would remove this sentence from the course...