In each case, draw a structure containing only carbon and hydrogen that satisfies the indicated criterion.

(a) A stable alkyne of five carbons containing a ring

(b) A chiral alkyne of six carbon atoms

(c) An alkyne of six carbon atoms that gives the same single product in its reaction either with BH₃ in THF followed by H₂O₂/^–OH or with H₂O/Hg²⁺/H₃O+

(d) A six-carbon alkyne that can exist as diastereomers