What defines a long-chain polymer?

A long-chain polymer is defined by a chain composed of smaller molecular units, known as monomers, which are chemically bonded together to form a larger and more complex structure. These polymers can vary significantly in length, and their properties are often determined by the arrangement and composition of these repeating units. In essence, the size and configuration of the polymer chain contribute to its characteristics, such as flexibility, strength, and durability.

This definition aligns with the understanding that polymers are large molecules that consist of repeating structural units, making the option that describes a chain composed of these units the correct choice. The other options do not accurately capture the essence of a long-chain polymer: a single unit of a chemical compound refers to a monomer, a mixture of adhesives does not specify a polymer structure, and a short repeating unit does not encompass the full, extended nature of long-chain polymers.