Step 1: Hybridisation of each carbon
\(C_2\) is part of the \(C=C\) double bond, so it is \(sp^2\). \(C_3\) is a CH\(_2\) with only single bonds, so it is \(sp^3\).
Step 2: Bond
The \(C_2-C_3\) bond is formed by \(sp^2\) and \(sp^3\) overlap. Option (D).
Final Answer:
The bond is \(sp^2-sp^3\), option (D).
\[ \boxed{\text{(D)}} \]