Which of the following sentences is correctly punctuated?

a. i shouldn't feel stress with only one final exam, but history is my hardest subject.

b. i have only one final exam it is in my history class.

c. i just really need to pass this class, i plan to graduate in june.

d. finals week is next week, i am already starting to feel stress.

d) the narrator even suggested that the white whale, moby d, was ubiquitous and present in every ocean at every moment.  

two factors or characteristics of a chapter that might make it difficult to read would be words i don't understand, or if i don't fully understand what's going on in the chapter. strategies i can use to get through the difficult material would be a dictionary, and re-reading previous chapters to get a better grasp of what the author is trying to say.