Which is the longest of the carbon-carbon single bonds indicated by arrows in the following compounds?
a. ⬇
HC≡C-C≡CH

b. ⬇
H₃C-CH₃

c. ⬇
H₃C-C≡CH

CH₂
d. ⬇//
H₃C-CH

e. H₂C
\\
HC-C≡CH