"It is an elephant!"
There is no equivalent structure in English, but try to think of це as "this is/these are." Here you'd be saying "This is is an elephant" if you added the є.
Remember, це is NOT a demonstrative adjective. If you want to say "this pen" or "these apples," you have to use a different word, цей, which declines to agree in number, gender, and case: ця ручка, ці яблука.