【单选题】Generally, in order to be preserved in the fossil record, organisms must possess hard body parts such as shells or bones. Soft, fleshy structures are quickly destroyed by predators pr decayed by bacte...
【简答题】English is now the international language for airline pilots, scientists, medical experts, businessmen and many others. Consequently, more and more people are learning it.
【简答题】C Medical experts say most Americans do not get enough sleep. They say more Americans need to take a nap — that is to rest for a short period in the middle of the day. They give people advice to sleep...