Fix grammatical mistakes in this sentence: Their name is not completely understood and difficult to trace back earlier than the 4th century AD, but it is possibly derived from the Proto-Turkic word *bulģha ("to mix", "shake", "stir") and its derivative bulgak ("revolt", "disorder").
Their name is not completely understood and difficult to trace back earlier than the 4th century AD, but it is possibly derived from the Proto-Turkic word *bulģha ("to mix", "shake", "stir") and its derivative *bulgak ("revolt", "disorder").