Without answering directly:
(31) To cross is to pass from one side to the other; to clear is to make empty; to do is to do anything at all; and to wipe is to rub, as for example with a cloth. What is the difference between a pen and an eraser or white-out?
(32) Abstractions differ, armies or fighters oppose, people disagree, and factions divide. Is an opinion an abstract thought or a person or group of people?
(33) In terms of time, "by" and "before" mark a moment in the future, "within" and "under" mark an interval. The phrase "within so much time" is adverbial, the phrase "under so much time" is nominal and requires another preposition if it is to be used adverbially, for example "in under two minutes". Eaten -- when? at a precise moment or during an interval? noun or adverb?
Student or Learner