I am pretty sure the abstract noun form for bore is boredom :)
The central idea is the same as the main idea. Most of the time, the main idea is mentioned in the Title. Without reading the essay, I do not know what the central/main idea is.
Of these four words, the one which is most likely to have a negative flavor or connotation is d)meander. To confuse is the state of being bewildered or unclear in one's mind about something. To distract is to the divided attention of an individual or a group away from the designated object on which the focus should be put on. A harangue is a long speech delivered in front of an audience. To meander is to walk around aimlessly without a fixed direction which contains a negative flavor or connotation.
I think it is compound or complex! Maybe, but it might be complex. I am 70% on the complex.
