台湾籍旅美老师今天交给我们的句子是：

How did eating popcorn become a custom at movie theaters? Nowadays, movie theaters depend on popcorn. They earn about 85 percent of their profits and forty percent of their total revenue from concessions. That was not always the case.
在电影院吃爆米花是怎么变成一种习俗的？时下的电影院靠着卖爆米花在赚钱，它们85%的利润及40%的总收入是来自贩卖部，但在过去却并非一直都是如此。

学习重点：

1.custom 习俗，惯例
custom (n.) 习俗，惯例
tradition (n.) 传统

2.nowadays 现今、时下
nowadays (adv.) 现今、时下
today (adv.) 现今、当代

3.profit 利润
profit (n.) 利润
profitable (adj.) 有利的

4.revenue 收入
revenue (n.) 收入
income (n.) 收入