The compound below is estradiol, a hormone that triggers the development of female secondary sex characteristics. "A structure with a hexagonal ring with points top and bottom and alternating double bonds is single bonded to O H at bottom left. A second hexagonal ring shares the right side of the first. A third hexagonal ring shares the upper right side of the second. A pentagonal ring shares the right side of the third hexagon. H is single bonded behind the lower left and lower right corners of the third hexagon, in front of the bottom point of the third hexagon, and in front of the upper right corner of the pentagon. A C H 3 is bonded in front of the upper right corner of the third hexagon.

Estradiol is best described as which of the following?
an alkyne
an alkene
an alkane
an aromatic