诶，嗨, 啦，吧，哦 and 啊
Chinese uses a number of particles to indicate the speakers attitude, to show surprise, excitement, disappointment etc. The particles appear either at the beginning or at the end of of an utterance. The majority of characters contain the 口 radical.
嗨 hāi - hey, hello
诶 ēi - expresses mild surprise
啦 lā - indicates excitement or doubt
吧 bā - indicates a suggestion or polite encouragement
哦 ō - indicates surprise, sudden understanding
啊 ā - indicates a range of attitudes (confirmation, impatience ...)