Hello there! I'm pretty sure the best answer is A. She wrote on everything she could find.
C doesn't have anything to do with her writing, and neither does D! B could potentially work as an answer, but A is a better, more solid answer since it show how often she loved to write :)
I would say the third option, as Fredrick Douglass wrote his as an autobiography, and Huckleberry Finn is an adventure-type story.
C. You need a comma when the sentence changes subjects from humans to bottlenose dolphins.