Question

the separation of the foci of an ellipse that describes a planet's orbit derermines
A eccentricity of the orbit
B period of the orbit
C size of the orbit
D all of the above.

I think it is A because the closer the foci, the more circular versus elliptical the orbit is.
Size is determined by the major axis. Period: square of the period is equal to the cube of the semi-major axis.
The foci are only mentioned in regards to shape/eccentricity.

Am I missing something? What can I research? Thank you for your help.