Which of the following is the correct equation for the distance formula for the points (x1, y1) and (x2,y2)?
A. D=sqrt (x2-x1)^2+(y2-y1)^2
B. D=sqrt (x2-y2)^2+(y1-x1)^2
C. D=sqrt -(y2-y1)^2+(x2-x1)^2
D. D=sqrt (x1-x2)^2+(y2-y1)^2