In fugal analysis, what is the opening theme called?

Question

I need help on this question from Grade 3 Music History.

Fugues - what is the opening theme called?

Answer 1

"A fugue opens with one main theme, the subject, which then sounds successively in each voice in imitation; when each voice has entered, the exposition is complete; this is occasionally followed by a connecting passage, or episode, developed from previously heard material; further "entries" of the subject then are heard in related keys. Episodes (if applicable) and entries are usually alternated until the "final entry" of the subject, by which point the music has returned to the opening key, or tonic, which is often followed by closing material, the coda. In this sense, fugue is a style of composition, rather than fixed structure."