Two central carbons are double bonded to each other; the pair is single bonded to C H 3 above left and right, and to H below left and right.
B
A skeletal model has line segments that slant up, down, up, and up again in a triple bond.
C
Two hexagon rings with carbons at each corner have alternating double bonds and share one side. H is single bonded to all the C's except the ones on the shared side.
D
Two carbons are triple bonded to each other; each has a single bond to the outside.