Which two forms of gustar are the only ones used most of the time? * gustar/gusta
gusta/gustan
gusto/gusta
gustas/gustan

And gustar has more the two forms (gusta and gustan).

Explanation:

As you can see, using gusta or gustan depends on the word that follows the verb. Depending on what you like, you choose the singular – gusta – or plural – gustan – form. Gustar can also be used in the infinitive form to talk about actions that we like. In this case, we will always use the singular form gusta.

what sentences? what words?