#english_language 

Non-essential clauses are clauses in a sentence that can be removed from it without affecting its essential meaning or grammatical structure. 
They are enclosed in [[Commas|commas]] OR [[Dashes|dashes]] OR parentheses (unless it's a transitional word like *however*). Dashes create a stronger break, parentheses imply that information is less important.

**THESE CLAUSES ARE INTRODUCED WITH "WHICH"**:

Farm animals, *which* were introduced to ...