1. Why do we say that someone who is fired gets the sack(麻袋)?
The ancient Romans didn't believe in mollycoddling(娇纵) convicted felons(重罪犯人). Rehabilitation(复原，昭雪) wasn't their style. Those convicted of parricide(杀近亲或长辈) or other heinous(及邪恶的) murders were tied in a sack and dumped into the Tiber River(台伯河), instantly solving any potential recidivism(累犯) problem. The practice spread throughout many other European countries, and, as late as the nineteenth century, murderers in Turkey were tossed into(投掷到) the Bosporus(博斯普鲁斯海峡) in a sack. To get the sack, then, probably was used figuratively(象征性地) as a threat of any sort of punishment, such as losing one's job.
Another theory to explain how get the sack was recorded — as early as 1611 in France — is that it referred to craftsmen(手艺人，工匠) of the Middle Ages. Artisans(技工) carried their tools in sacks; while they worked, they handed the sacks to their employers. When a craftsman got the sack, it meant that his services no longer were required. He was left, literally, holding the bag.