Tom has three good friends. They are Jack, David and Mark. They have different hobbies. Tom likes football. He often plays football on weekends. He thinks playing football can make him strong and healthy. He is in the school football team.

    Jack doesn't like sports. He likes listening to music. He likes Jay Chow best of all the singers. He has many of his CDs. He often listens to music on the way. He thinks music can let him feel happy.

    David doesn't like sports or music. He likes stamps. He collects stamps for five years. The stamps are very beautiful. He thinks collecting stamps can help him know more about the world.

    Mark likes taking photos. He has a few cameras. When he is free, he often takes out his camera and takes some pictures. Some of his pictures are in the newspapers. He thinks the world is beautiful. He wants to show the beauty of the world to others.

当前，不少农民购物时不太关注食品的品牌、质量、保质期等，问题食品充斥农村市场。导致这一现象的原因有（    ）

①不少农村消费者的安全权被侵犯  

②执法部门对农村市场监管力度不够

③不少农村消费者缺乏安全消费知识 

④某些生产者和经营者唯利是图

下列各句中，划线的成语使用不恰当的一句是(    )

世界上人口最多的大洲是（　　）