Thoureau wanted to poit to the fact that following traditions limits us and deprives us from developing our imgination. Thoreau, like other romantic authors, does not agree with tradition. He thinks it prevents people from finding true greatness and blocks their path to spirituality. "Castles in the air" are simply illusions by which people persuade themselves in something that is not true, in Thoureau's opinion.
The correct answer is B) "Bought grain, stored it, and resold it during times of low harvest":
Following a tendency of nationalizing several industries, which included salt, iron, and liquor, emperor Wu decided to interfere with the trade of grain in 110 BC. This happened as a response from the government to eliminate speculation generated by merchants by selling previously stored grain at below-market prices.
The primary way in which the passage of the Factory Acts (1844–1847) affected labor was that it restricted the working hours in factories to 10 hours a day, which cut back on worker injury and fatigue.