Since all triangles' angles have a sum of 180 degrees, it can't be A, because that would make it 240 degrees. That leaves us with B and C. While B <em>could</em> be true, we don't know it for sure. Therefore, C is the correct answer because adding them should equal 60 degrees, which, adding them to the first angle (which was 120 degrees), would 180 degrees.
