复数)are 2.am(复数)are 3.are(单数)is 4.library(复数)libraries 5.story(复数)stories 6.factory(复数)factories 7.body(复数)bodies 8.hobby(复数)hobbies 9.people(复数)people 10.fish(复数)fish 11.policeman(复数)policemen 12.city(复数)cities 13.firemen(复数)fire