PLZ HELP WILL GIVE BRAINLY FOR CORRECT ANSWER

Read the following sentences.

The news report was exciting. A flash mob in costumes had ridden bicycles through town.

Which of the following correctly combines these two sentences into a complex sentence?

A.
The news report was exciting; a flash mob in costumes had ridden bicycles through town.
B.
The news report was exciting, for a flash mob in costumes had ridden bicycles through town.
C.
The news report was exciting because a flash mob in costumes had ridden bicycles through town.
D.
The news report was exciting, a flash mob in costumes had ridden bicycles through town.