Which statement describes the effect on the parabola with an equation of \( y = x ^ { 2 } - 2 x \) when it is changed to \( y = x ^ { 2 } + 2 x ? \)
A. The parabola is shifted to the left \( 2 \) units.
B. The parabola is shifted to the right \( 2 \) units.
C. The parabola is shifted to the left \( 4 \) units.
D. The parabola is shifted to the right \( 4 \) units.