156. A 2008 study by two Harvard economists notes that the "labor-market premium to skill"—or the amount college graduates earned that's greater than what high-school graduate earned—decreased for much of the 20th century, but has come back with a vengeance (报复性地) since the 1980s.
译文
两位哈佛经济学家在一份2008年的研究中指出,“劳力市场给予技术的补贴”——或者说,大学毕业生与高中毕业生的收入差距——在20世纪大多数时间里缩小了,但从20世纪80年代起这种差距又报复性地拉大了。
点睛
本句的主干是...study...notes that...。第一个that引导的宾语从句that the "labor-market..."...since the 1980s作notes的宾语。该从句中又包含多重从句,其主干为the "labor-market premium to skill" decreased, but has come back;两个破折号之间的内容则对labor-market premium to skill进行补充说明,在该部分中,两个定语从句college graduates earned和that's greater than what high-school graduate earned 均修饰the amount。
premium意为“酬金,额外费用”。vengeance意为“报仇,复仇”。decrease意为“下降,减少”。如:
Our company tries to decrease the costs. 我们公司设法降低成本。
考点归纳
decrease、lessen、diminish和reduce这组动词的一般含义为“减少”。decrease和lessen比较普通,一般可以代替这组词中的任何其他词。

decrease强调数目逐渐减少或情感逐渐减退。如:
My interest in online shopping gradually decreases. 我对网上购物的兴趣逐渐减退。

lessen与decrease近义,指数目、程度、价值、实力等的减少。如:
The cancer patient has to take painkillers / turn to drugs to lessen his pain. 癌症病人靠吃止痛药来减轻痛苦。

diminish表示减少损失。如:
We must diminish the cost of production. 我们必须缩减生产成本。

reduce可以表示尺寸、数量、程度或强度的减少,也可以表示地位、处境、状况的降低。如:
The landlady won't reduce the rent of our house. 女房东不肯减收我们的房租。
The bankrupt was reduced to despair. 破产者陷入了绝望。