What is a complex sentence?
a. a sentence with no subject
b. a sentence that consists of one independent clause
c. a sentence that contains both an independent clause and one or more subordinate clauses
d. a group of words containing a subject and a verb that cannot stand alone as a complete sentence?

The correct answer among all of the given choices from my personal knowledge would be:

C. A sentence that contains both: an independent clause and one or more subordinate clauses.

My reasoning behind this: A complex sentence is made up of a subordinate clause or clauses.

I hope this is the answer you were looking for and that it helps!! :)

Hope i can you!