It can be seen from the quadratic function equation that when y=4, x 1=2009 and x2=20 10, the distance between two points is exactly 1 unit.

When the intersection of the image and the X axis is y=0, the distance between two X points is required to be 1 unit, so after translation,

When y' = y-4 = 0, x 1'=2009 and x2' = 20 10.

That is, it has dropped by 4 units.

Because it is a multiple-choice question, not a calculation question, the calculation will not be very complicated, and generally there will be simple skills. The equation given in this question is a reminder.