Unit 5Plus and minusDo some maths work10+5=? 20-11=?9+7=? 13-6=?8+12=? 17-9=?13+5=? 19-15=?111213151617181920one rubbertwo rubbersone bookfive booksone bikeseven bikesone peachfour peachesone orangeeight orangesone keyten keysone carthree carsone knifeeleven knivesone busfour buses 1) 一般情况 加 –s 1.清辅音后读/s/; book-bo..