Afer some time passed, baseball's second league was created is this a simple, compound or complex sentence

This sentence is complex.
Complex sentences consist of a dependent and an independent clause, as is the case here. The dependent clause is After some time passed, and the independent one is the rest of the sentence. 
A simple sentence would have only one independent clause, and a compound sentence would have at least two independent clauses. 

Ithink your answer is d