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According to a Bengali proverb "Janma.Mrityu, Biye....Teen bidhata niye " i. e. The tree events of birth,Death and Marriage are in the hands of GOD ,hence unpredictable. So tree events birth ,death and marriage are unpredictable.
Three things that are unpredictable are Cloud,Crop and Cup.
Three nature that are unpredictable are Earth quake, Flood and Volcanic eruption.
Three subjects that are unpredictable are History,Geography and Economics.......and so on and so on...