Select the sentence below that uses proper punctuation to separate a nonessential phrase from the main sentence. a. pocahontas saw a man with yellow hair walking through the forest — a sight she had never seen before — so she followed him. b. pocahontas saw a man — with yellow hair — walking through the forest a sight she had never seen before so she followed him. c. pocahontas saw a man with yellow hair — walking through the forest — a sight she had never seen before so she followed him. d. pocahontas saw a man with yellow hair walking through the forest a sight she had never seen before — so she followed him.

The correct option is A.
A non essential phrase is a phrase that can be removed from a sentence without changing the meaning of the sentence. Non essential phrases usually give unimportant information and details that one can easily do without. Commas are usually used to set off non essential phrases. 
In the sentence given above, the non essential phrase in the sentence is 'A sight she had never seen before'.  If this phrase is removed from the sentence, the idea in the sentence will still remain the same and the sentence will read: 'Pocahontas saw a man will yellow hair walking through the forest so she followed him. 
There is also essential phrase; if an essential phrase is removed from a sentence, the main idea of the sentence will change.

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