VOA慢速英语:咖啡为伦敦公车提供动力

cup - n. a small round container that often has a handle and that is used for drinking liquids (such as tea and coffee)

emissions - n. something sent out or given off

chain - n. a group of businesses (such as stores, restaurants, or hotels) that have the same name and basic appearance and sell the same products or services

untapped - adj. available but not used (untapped resources)

discourage - v. to try to make people not want to do (something)