When Mercury Is at Greatest Elongation It Is Sometimes at a More

When Mercury is at greatest elongation it is sometimes at a more favorable position for viewing and sometimes at a less favorable position for viewing. What can change from one occurrence of greatest elongation to the next to cause this difference?

A) the eccentricity of Mercury's orbit
B) the inclination of Mercury's orbit relative to the ecliptic
C) the position of Mercury in its orbit
D) the direction in space of the semimajor axis of Mercury's orbit