Which statement correctly describes the effect of the parabola y=x^2+2x when it is changed to y=x^2+4x?
A: The parabola is translated to the right by two units.
B:The parabola is translated two units to the left and 4 units down.
C:The parabola is translated 1 unit to the left and 3 units down.
D: The parabola is vertically stretched by a factor of 2.
E: The parabola is vertically compressed by a factor of 2.