

この川で泳ぐのはきけんです。
この道は夜もきけんですか。
きけんな場所には行かないでください。
"きけんな(危険な)" is in the lesson "Adjectives 2" (Level 4), along with 17 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.