Basically, Chinese meaning is also related to the tone you use in your speech. eg. if the tone is rising, it should be a question, if the tone is falling, it can be statement or complaining or conjecture. For the above ending syllables, my view is: 啦 can be question or statement, which depends on the tone (rising is question, falling is statement)n eg. 看见啦？（see?）好啦！（OK） 呢 is usually the ending of question. eg. 你呢？（and you?） 啊 is usually the ending of interjectional sentence. eg.真快啊！（it's so fast!） 吧 is usually the ending of conjecture. eg. 你是Mary吧，对吗？（You're Mary, aren't you?） 哦 usually means "I understand", especially in the MSN or QQ chatting, people can say 哦 means "I understand" just like "Oh" in English.