In the image, point a marks the center of the circle.
which two lengths must form a ratio of 1: 2?
a)af: ae
b)bc: ef
c)ef: ah
d)ah: ef
e)ah: ad

I would go with D) AH:EF. The easiest relationship among the parts of a circle that would have the ratio of 1:2 would be that of a radius to a diameter. Among the choices, the one that matches the 1:2 ratio would be AH (a radius) and EF (a diameter).

Agc and bgd are vertical angles