Answer:
Complex
Step-by-step explanation:
Complex sentence is a sentence that contains an independent clause and at least one dependent clause.
The independent clauses can stand alone and give a full thought while the dependent clause cannot give a complete thought.
From the answer, we discover that:
"Variations of bowling have existed for centuries" is an independent clause and makes a complete thought while
"...but a standard form of the game wasn't established until various regional bowling clubs formed the American Bowling." is the dependent clause which gives an incomplete thought.
The above answer is correct.