The piece of cloth will do ___ a turban.

The correct answer is for. The phrase "do for" in this context means "to serve as" or "to be sufficient for a particular purpose." So, "The piece of cloth will do for a turban" means the cloth is suitable or sufficient to be made into a turban. Options A ("to"), C ("by"), and D ("with") are incorrect because they do not form a grammatically correct or contextually meaningful phrasal verb in this sentence. "Do to" implies an action performed on something, "do by" implies treatment, and "do with" implies handling or managing.