Propose at least two different structures for a compound with six carbon atoms that exhibits the following features:

a. All six carbon atoms are sp² hybridized.

b. Only one carbon atom is sp hybridized, and the remaining five carbon atoms are all sp³ hybridized (remember that your compound can have elements other than carbon and hydrogen).

c. There is a ring, and all of the carbon atoms are sp³ hybridized.

d. All six carbon atoms are sp hybridized, and the compound contains no hydrogen atoms (remember that a triple bond is linear and therefore cannot be incorporated into a ring of six carbon atoms).