Marta is the subject of the sentence because she is performing the verb "Planned"
I would definitely go with C. a topic sentence. While A. is never a bad idea, essay paragraphs tend to get marked as off topic if there is not a topic sentence. Hope this is helpful!
- the author is limited to what he or she can make the characters do, in a way this affects the characters as well
- in different settings the characters may live different lives due to the environment they live in
- If it is a made up location then the author can do whatever he or she pleases, but if it is a real life location then they have to base the surroundings off of that area
Here are some I could think of hope this helps:)