人教高三大题优练5 七选五 说明文 教师版.docx

七选五之说明文
大题优练5
优选例题
【例题1】
You run into the grocery store to pick up one bottle of water. You get what you need, head to the front, and choose the line that looks fastest.
You chose wrong. People who you swear got in other lines long after you are already checked out and off to the parking lot. 1
It turns out that it’s just math working against you; chances are that the other line really is faster.
Grocery stores try to have enough employees at checkout to get all their customers through with minimum delay. 2 Any small interruption — a price check, a chatty customer-can have downstream effects, holding up an entire line.
If there are three lines in the store, delays will happen randomly at different registers. Think about the probability: 3 So it’s not just in your mind: Another line probably is moving faster.
Researchers have a good way to deal with this problem. Make all customers stand in one long, snaking line — called a serpentine line — and serve each person at the front with the next available register. 4 This is what they do at most banks and fast-food restaurants. With a serpentine line, a long delay at one register won’t unfairly punish the people who lined up behind it. Instead, it will make everyone slow down a little bit but speed up checkout overall.
5 It takes many registers to keep one line moving quickl