ACT English prep 2015/16 ..can u guys help me with this question

Above the columns extends a horizontal stone band called a frieze; carved into it are the classical theatrical masks that represent comedy and tragedy.

*the phrase enclosed by the two asterisks is the underlined part.

F. NO Change is the answer …I don’t get why that’s the answer though.
I thought we use a comma here not a semi-colon.

A semicolon is the same as a period. Those are two complete sentences.

You can’t put a comma between two complete sentences.

You may be confused because the independent clause after the semicolon displays subject-verb inversion: its subject is “the classical theatrical masks that represent comedy and tragedy” and its verb is “carved.”

Thanks. I will take a look at subject-verb inversion.