what kind of compound can form polymer by itself?

AQA a level chemistry 2017 paper 3 Q25
Which compound can form a polymer without needing another reagent?

A HOCH2CH2OH
B HOOCCH2CH2COOH
C HOCH2CH2COCl
D ClCH2CH2COOH

The answer is C, that i assume ester and HCl were formed. Hence, would like to know why D cannot form a polymer by itself? (can't it also form HCl and ester at for product?)

were there any condition for compound to form polymer?

To make an ester, you need an alcohol (or phenol) and a carboxylic acid (or acyl chloride or acid anhydride). D has the acid end, but has a halogen at t'other end.

compound D have halogen ( ClCH2CH2COOH) it have Cl and COOH at the end. which Cl is halogen.

If one end of the molecule has COOH and the other end has OH, then the COOH of of molecule can esterify with the OH end of another. There is still an OH and a COOH at either end of this combined molecule, so can esterify again and again.

as you mantioned COOH and OH can bond together which gives out ester, so why B can't from polymer by itself? Also D can't ester polymer form also taking out HCl same as C?