you can't usually hear the s on livre or pomme, but you can (or at least I can) hear the difference between le and les. Le = Luh and Les = Lay, once you hear the "lay" sound, you know it must be plural... I think that's right at least!
Listen to the articles. Le or les, la or les. Use the slow version everytime that you see these words until it sounds clear to you. *also, the chapter is plurals so you should be expecting plural words to be used.