几个单词单数变复数的问题

题目

几个单词单数变复数的问题
cat
brother classroom fun he factory
key hurse flag map （a botble of milk ）一个
（piece of peper） （ a man teacher ）
（an apple tree ）

答案

cats
brothers
classrooms
funs
they
factories
keys
hurses
flags
maps
bottles of milk
pieces of paper
men teachers
apple trees