Before the car wash, Tanya made signs and Gabe signed up volunteers.
is it a Simple Sentence
Compound Sentence
Complex Sentence
Compound-Complex Sentence?

The correct answer is D. Compound-complex sentence

Explanation:

Complex sentences different from simple or compound sentences always include a dependent clause connected to an independent clause. In the case of the sentence presented "Before the car wash" is the dependent clause because this does not express a complete idea and includes the word "before" that is a subordinating conjunction and "Tanya made signs and Gabe signed up volunteers" is the independent clause as this expresses a complete thought. Besides this, a sentence is compound if two ideas of the same importance are included and joined by a conjunction such as and, or, but, which occurs in "Tanya made signs and Gabe signed up volunteers". This means the sentence includes the elements of a complex sentence (independent-dependent clause) and a compound sentence (two independent clauses) and therefore it is a compound-complex sentence.