Provide an Appropriate Response $x ^ { 2 } - x y + y ^ { 2 } = 4$

Multiple Choice

Provide an appropriate response.
-At the two points where the curve $x ^ { 2 } - x y + y ^ { 2 } = 4$ crosses the $x$ -axis, the tangents to the curve are parallel. What is the common slope of these tangents?

A) 1
B) -1
C) 2
D) -2