

Кефир — очень полезный напиток.
Kefir is a very healthy drink.
Это полезный сок?
Is this juice healthy?
Сладкий лимонад — не полезный напиток.
Sweet lemonade isn't a healthy drink.
"полезный" is in the lesson "Drinks" (Level 40), along with 11 other useful words. LinDuo has 180 topic lessons like this one, 2,380 words in total. Every word has an illustration, a transcription and pronunciation in a female and a male voice. Just 10–15 minutes a day is enough to learn them all. Free, and works offline.