A simple sentence has only one independent clause. A compound sentence has at least two independent clauses. A complex sentence has one independent clause and at least one dependent. A compound-complex sentence has at least two independent clauses and one dependent.
Having this in mind, 1. is a complex sentence, and 2. is also a complex sentence.
These are some of the most significant economic factors behind the stock market crash of 1929.
I believe it would be D. ..
Its very hard to make a hook/intro without the basic outline/body
You don't have to worry about punctuation or spelling in a rough/first draft
You can always revise and make the tone more in with the subject.
First draft you would be mainly writing down all the information/ thoughts in your mind so you can look back and go through and decide whats more appropriate for your topic