经济学词汇是这篇lecture的最大特点，朗读复述下列句子，对于经济学的话题有所帮助。
1) Of course, booms aren’t always followed by busts.We’ve certainly seen times whenlocal economies expanded rapidly for a while and then went back to a normal pace of growth.
2)But, there’s a type of rapid expansion, what might be called the hysterical orirrational boom that pretty much always leads toa bust.
3)See,people often create and intensify a boom when they get carried away by some new industry that seems like it will make them lots of money fast.
4)So,here we’ve got all the conditions for an irrational boom: a prospering economy, so more people had more disposable income-money to spend on luxuries,but they weren’t experienced at investing their new wealth.
5)As demand grew, people began selling promissory notes guaranteeing the future delivery of priced tulip bulbs. The buyers of these pieces of paper would resell the notesand mark up prices.
6) These promissory notes kept changing hands from buyer to buyer untilthe tulip was ready for delivery.
7) But it was all pure speculation because as I said, there was noway to know if the bulb was really going to produce the variety, the color thatwas promised.
8) And people were borrowing, mortgaging their homes in many cases to obtain those bits of paper because they were sure they’d find an easy way to make money.