[ao],[ou],[iu]都是复韵母。前一个元音开口度大，发音长而响；后一个元音开口度小，发音短而轻，比较模糊。从前一个元音到后一个元音是自然滑行，不能跳跃。 [ao],[ou],[iu] are all compound finals. In each of them, the former vowel is more open, longer and louder while the latter one is narrow, short, weak and blurred. It is imperative to have a natural glide but not a sudden change from the former to the latter.

[ao],[ou],[iu]都是复韵母。前一个元音开口度大，发音长而响；后一个元音开口度小，发音短而轻，比较模糊。从前一个元音到后一个元音是自然滑行，不能跳跃。 [ao],[ou],[iu] are all compound finals. In each of them, the former vowel is more open, longer and louder while the latter one is narrow, short, weak and blurred. It is imperative to have a natural glide but not a sudden change from the former to the latter.