不可数名词都默认为单数，所以总是用is或者was。 如何加后缀：
a.一般情况下，直接加-s，如：book-books, bag-bags, cat-cats, bed-beds
b.以s. x. sh. ch结尾，加-es，如：bus-buses, box-boxes, brush-brushes,watch-watches
c.以“辅音字母+y”结尾，变y为i, 再加-es，如：family-families, strawberry-strawberries
d.以“f或fe”结尾，变f或fe为v, 再加-es，如：knife-knives
e.不规则名词复数： man-men, woman-women, policeman-policemen, policewoman-policewomen,mouse-mice child-children foot-feet ,.tooth-teeth fish-fish, people-people,Chinese-Chinese, Japanese-Japanese