

この町の主な産業は観光です。
会議の主な目的は何ですか。
このレストランの主なお客さんは学生です。
"おもな(主な)" is in the lesson "Adjectives 6" (Level 40), along with 10 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.