Since a radius needs to appear first on the list, it is worthwhile to identify those segments that are radii. A radius extends from the center (O) to a point on the circle. OG and OD are the only ones. The selected answer is the only one that has one of those listed first.
A chord is a line segment whose ends are points on the circle. There are 4 chords in the figure, one of which is also a diameter:
... DG, DH, FG, FH . . . . DG is also a diameter, since it includes the center point, O
There is one tangent: DE, an external line that intersects the circle at one point.
It's c. the only way he can compare both is by calculating both groups' mean and comparing it. Randomizing wont work because it is mixing both protein bar users and non-protein bar players.