Though it is generally accepted that junk food is not healthful, American fast-food restaurants are popping up all over the world. These restaurants are for people who are always in a rush. If they don't have time to sit down to a regular meal, they race over to the nearest McDonald's. There they can quickly satisfy their hunger.
    Because Americans like things done immediately, they often order their food quickly at fast-food restaurants. They say, "A burger, fries and a coke!" though it's not polite, it's efficient. So when you are in the States, try to order this way. After all, in America do as the Americans do.

be hard-pressed for time/money  时间/金钱不够用
fast-paced  快步调的
junk food  n. 垃圾食品，无营养食品
pop up  v.突然出现，蹦出
mushroom  n.香菇  v.雨后春笋
be in a rush = be in a hurry = on the go(口语,忙碌)
a chain of restaurants  n.连锁店      v. I chained him to the tree.
satisfy one's hunger/thirst  填饱肚子，止渴
quench one's thirst  止渴
a coke (口) = a can of coke
In rome do as the romans do