Simple because it has one subject
As for the first part, Cost, Radiation exposure to humans, No water or heat, and unfit soil. As for the second, Astronomers, Botanists, and obviously your fair share of rocket scientists and math matitions for the way up.
B is the correct answer because their is already plural so you don't put an apostrophe any where in it.
B. A character who undergoes an internal change over the course of the story.
