Several points help to make this sentence clear. The "mores" of a society are its general customs. This word is related to "morals," though "morals" has a greater ethical content in its notion than does "mores." Secondly, the fact that such people are looking to do something "through revolution" implies that they are not undertaking their actions through peaceful means. This helps us to eliminate the options for the third blank that are too "calm" and reform-minded (as opposed to openly revolutionary). Hence, "overthrow" is excellent. Such people are likely questioning the accepted mores of the community. In a way, "accepted mores" is a bit redundant, but the expression does help to stress the fact that these revolutionaries are acting against the established order of things. Such people who wish to "tear down" the accepted order are called "iconoclastic." An "icon" is a likeness or image. The word "icono-clast" literally means the breaker of an icon. (This comes, in part, from a position in the Christian community that wished to destroy all images.) In general, "iconoclastic" signifies the outlook that would destroy or uproot established institutions.

You are told that the professor is very old and that whatever action he is doing he goes "on and on." Because he is giving a lecture it makes sense that he is speaking, and from context you can infer it is a word that means speaking in a long-winded and boring fashion. The correct answer is therefore "droned," although "rambled" and "prattled" could also be acceptable answers as these words have similar meanings. Additionally, you are told that the professor "only paused" meaning the adjective used to describe his pauses is most likely something like occasionally. The correct answer is therefore "intermittently." Finally, the professor gives a glance to his students. The word "glance" suggests a quick look so the correct answer is "perfunctory" which means quick, brief, and cursory. To provide additional help, "ensconced" means hidden, settled; "haughtily" means done with arrogance; "impolitic" means not polite; "mournful" means full of sadness; "lampooned" means mocked; "amiable" means friendly and sociable. 

You are told that the boy is "mischievous" and pulled a prank. The conjunction "but" is also a relevant clue to the context of the sentence. From this information you can infer that the boy would want to hide or conceal his grin so as not to give away the prank. The correct answer is therefore "stifle." The word "but" suggests that the boy's attempts to "stifle" his grin were not successful, so the correct answer must be that his smile was enhanced or "augmented" by seeing his prank unfold. To provide additional help, "complacent" means lazy, careless; "amplify" means enhance; "diminish" means take away from, reduce in importance; "cantankerous" means grumpy; "serene" means peaceful; "demonize" means portray as evil; "remedy" means fix; "harmonize" means coordinate, make something fit with something else; "whimsical" means silly or quirky; "antagonize" means annoy, make angry; "contentious" means debatable; "admonish" means chastise, tell off.