HSK 6
Shānqū tiānqì biànhuà-wúcháng, chūxíng yào dài sǎn.
Weather in the mountains is unpredictable - bring an umbrella.
HSK 6
Tā de qíngxù biànhuà-wúcháng, nányǐ xiāngchǔ.
His moods are unpredictable - he's hard to get along with.
HSK 7-9
Gǔshì biànhuà-wúcháng, tóuzī xū jǐnshèn.
The stock market is volatile - invest with caution.