We'd sooner say "Which sentence is correct?" or "Which option is correct?" In English, we don't use "variant" as much as Russians do; it has more of a technical meaning in English. I'll rewrite your sentences, to show how I'd naturally express them. 1. I'm not interested in sport anymore. / I'm no longer interested in sport. 2. Sport does not interest me (anymore). 3. I don't like sport. 4. I've stopped enjoying sport. The use of "now" is either unnecessary or a bit awkward. The verb is already in a present tense, so there's not really any need to add "now". I suggest looking up the difference in using sport/sports. Both are correct, but certain speakers have a preference for one over the other. I hope this helps a bit.

Which variant is correct 3 is the only one which is in English