

おー、すごいですね!
おー、田中さん!久しぶり。
おー、もう宿題が終わったの?
"おー" is in the lesson "Conversation" (Level 36), along with 15 other useful words. LinDuo has 180 topic lessons like this one, 2,379 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.