The ability of certain hormones to attach to a cell is primarily determined by the

Receptor molecules in the cell membrane.  

Explanation:

Very small amounts of hormones can trigger very large responses in the body. This is because hormones bind to receptors located on or inside the cell membrane. The binding of a hormone to a receptor accelerates, reduces or alters cellular function in another way. Ultimately, hormones control the function of whole organs.

They control growth and development, reproduction and sexual characteristics. They influence the way the body uses and stores energy. In addition, hormones control fluid volume and salt and blood sugar concentrations. Some hormones affect only one or two organs, while others affect the whole organism.

it enhances antibody production by t cells of the adaptive immune system.

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explanation:

the answer to your question is:

c. complementary base-pairing