The Horse and the Dog（在线收听）

    A dog and a horse，which served the same peasant，began to discuss each other's merits，one day．“How grand we are，to be sure！”says Barbos．“I shouldn't besorry if they were to turn you out of the farmyard．A noble service，indeed，to plough or to draw a cart！And I've never heard of any other proof of your merit．How can you possible compare yourself with me？I rest neither by day nor by night．In the daytime I watch the cattle in the meadows；by night I guard the house．”
    “Quite true，”replied the horse．“What you say is perfectly correct．Only remember that，if it weren't for my ploughing，you wouldn't have anything at all to guard here．”
    Exercises：
    回答下列问题：
    ① What did the dog and the horse begin to discuss？