Is the sentence carol enjoys rollerblading so she bought a new helmet a complex or compound or simple sentence?
This sentence is definitely not a simple sentence, because it contains two complete clauses. If "so" is acceptable as a coordinating conjunction, this is a compound sentence, …but if "so" is regarded as necessarily a subordinating conjunction as it usually was before about 1960, it is a less than optimally expressed complex sentence. For the old-fashioned, it should preferably be reworded as "Because Carol enjoys rollerblading, she bought a new helmet." (MORE)