Which of the following statements is true regarding the formation of polymers?

Polymer formation can occur through various mechanisms, and one common method is the condensation reaction. In this process, monomers join together to form larger molecules, or polymers, along with the release of small molecules, typically water. This is characteristic of condensation polymerization, where each time a bond is formed between monomers, a small molecule is expelled. This aspect establishes the correct answer, as the formation of many types of polymers indeed involves the loss of small molecules.

In contrast, the other statements do not hold true for all polymers. For instance, monomers usually change their structure when they polymerize; thus, they do not retain their original structure. Additionally, while many polymers contain carbon atoms linked by single bonds, they often also feature double bonds or other functional groups. Finally, while alkenes can be involved in polymer formation, they typically undergo addition reactions rather than condensation; hence, not all polymers result specifically from condensation reactions of alkenes. Overall, statement A accurately describes a fundamental aspect of polymer chemistry.