呃:
1.hiccough
2. HAW
3. Ur
4. eh
Examples:
他说："老兄，原来你在这里，你还活着吗，呃？"
"So there you are, old chap, still in the land of the living, eh? " he said.
啊:
1. ah
2. (interj.)
Examples:
啊，你在这里呀！
Ah, there you are!
哦！天啊！我英文没有考及格！
Oh, dear! I failed in the English examination!
啊，好啦，一样白米养百样人嘛。
Ah, well, it take all kinds!
4. 啊，我真喜欢这首歌！好高兴！
Ah, I really love this song! I am so glad!
5. 多可爱的婴儿啊!
Isn't that baby a dear?