Common structural feature: sigma bonds

Steps:

• Identify ethene (C₂H₄) as having C=C double bonds with one σ and one π bond, sp² hybridization, and 120° angles.
• Identify polythene [(-CH₂-CH₂-)ₙ] as a polymer with only C-C single bonds (σ bonds), sp³ hybridization, and 109.5° angles.
• Compare features: both contain C-C and C-H σ bonds; ethene has π bonds, polythene does not.
• Eliminate options lacking commonality: π bonds, 109° angles, and sp orbitals are unique to one.

Why A is correct:

• σ bonds form the backbone of all C-C and C-H connections in both ethene's double bond and polythene's chain, per VSEPR theory.

Why the others are wrong:

• B: π bonds exist only in ethene's double bond, absent in polythene's single bonds.
• C: 109° angles occur in polythene's tetrahedral sp³ carbons, but ethene has trigonal planar 120° angles.
• D: sp orbitals are not present; ethene uses sp², polythene uses sp³.

Final answer: A