The correct answer to your question is "An independent clause and a dependent clause"
When I was in middle school I was taught that there is an easy way to remember the formula for a complex sentence. My teacher always told us, “a complex sentence, isn't all that complex.”
It is simply one independent clause and one dependent clause.
An independent clause can stand alone as a sentence, so basically an independent clause is a simple sentence. As the word “independent” implies it is okay on its own, like an adult.
A dependent clause on the other hand, cannot stand on its own. Like a kid depending on their parents, the dependent clause depends on independent clauses to be part of a sentence.
These clauses need to be joined by something, like a comma or a conjunction.
I have provided an example for future reference:
I burnt the bread but not the pasta! (Inspired by my mom's cooking skills.)
In this example, "I burnt the bread" is the independent clause. It doesn't need anything else to be a full sentence. The dependent clause is "but not the pasta," because this clause couldn't stand on it's own. In this example I connected my clauses with the conjunction “but” which becomes part of the dependent clause.
They do not always have to be in that order, the dependent clause can come first in some instances. Such as when you start with a prepositional phrase.
Here’s an example: “In the future, I want to be president.”