Which statement about the orbit of the earth is correct?
选项：

A: The orbit of the earth around the sun is an ellipse with the sun as one of the foci
B: The orbit of the earth around the sun is an ellipse with the sun at a point halfway between the two foci
C: The orbit of the earth is a circle with the sun at a point next to its centre
D: The orbit of the earth around the sun is a circle with the sun at its centre