In the Path of Mars Against the Background Stars Shown

In the path of Mars against the background stars shown in Figure 2-2 in Comins,Discovering the Essential Universe,6th ed.,the planet appears from Earth to move in a loop,moving westward for a period of time.What is the angle between the Earth-Sun line and the Earth-Mars line when the planet is halfway through the retrograde motion,on about February 1?

A) 180°
B) It can be any angle.
C) 0°
D) 90°