What is the complete subject of sentence singers in an opera sometimes sing different languages?

The complete subject of the sentence "Singers in an opera sometimes sing different languages" is singers in an opera.

Here's why:

* Subject: The subject of a sentence is the person, place, or thing that performs the action of the verb. In this case, the singers are the ones performing the action of "singing".

* Complete Subject: The complete subject includes all the words that modify or describe the subject. In this case, "in an opera" tells us where the singers are singing, further defining the subject.