For Each of the Following Sentences, Fill in the Blanks

For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below.Not all words or phrases will be used; each word or phrase should be used only once.
$\begin{array}{lll}\text { affinity } & \text { billions } & \text { ligands } \\\text { antibodies } & \text { coiled-coils } & \text { loops } \\\text { antigens } & \text { hundreds } & \text { size-exclusion } \\\beta \text { strands } & \text { ion-exchange } &\end{array}$

The human immune system produces __________ of different immunoglobulins, also called __________, which enable the immune system to recognize and fight germs by specifically binding one or a few related __________.The hypervariable structural element that forms the ligand-binding site is comprised of several __________.Purified antibodies are useful for a variety of experimental purposes, including protein purification using __________ chromatography.