The question asks: Which substrate will most readily give the dehydrohalogenation product?

However, the actual structures/options A, B, C, D are missing in the prompt. Since dehydrohalogenation depends critically on the structure of the haloalkane—such as:

1. degree of substitution of the carbon bearing halogen,
2. possibility of forming a more substituted alkene,
3. stereochemical requirement for elimination,
4. stability of the alkene formed,
5. whether the mechanism is $E1$ or $E2$,

it is not possible to derive the correct answer rigorously without the given options.

General principle

In general, dehydrohalogenation occurs most readily for substrates that:

1. can eliminate to give the most stable alkene,
2. are often tertiary alkyl halides (especially under alcoholic KOH conditions),
3. may proceed via $E1$ if a stable carbocation can form, or via $E2$ if there is a suitable $\beta$-hydrogen and proper geometry.

Thus, among typical options, the compound that most easily undergoes elimination is often the one that is tertiary or gives a highly substituted alkene.

About the stored answer

The stored correct answer is given as D, but since the actual structures are absent, I cannot independently verify whether $D$ is truly correct.

So the only academically honest conclusion is:

• the problem is incomplete, and
• the answer cannot be confirmed from the provided data.

If you share the structures for options $A, B, C,$ and $D$, I can solve it properly and verify whether $D$ is correct.