The correct answer is B. During the prewriting stage, it is important to come up with a theme for the story.
When you are prewriting, you are deciding on what you actually want to write about - in this stage, you should think about the topic, the themes, the characters, and give your story an outline that you are going to decorate with details later on.
A is incorrect because both can be long or short, depending on your inspiration. C is incorrect because it is the other way round. D is incorrect because you decide on this during the prewriting stage, not after.
Journalist, soldier, river boat pilot
The correct answer is D, because there are three independent clauses in this sentence, all of the clauses are independent. A means that there is at least one dependent clause, which is not the case here, and B means the same. C mean that there is only one independent clause in the sentence.
