在等差数列{a_n}中，若a₂=5，a₁₀=21，则a₆等于（　　）

下列关于资源的叙述正确的是(    )

    Hello!My name is Bob. My classroom is not big but nice. There are 21 desks and 20 chairs. 墙上有一些画和一幅地图。Mrs Brown is our English teacher. She is from a big city.She is nice. Her husband Mr Brown is a teacher too, but he isn't in our school. Tom is my good friend. We like playing football on Saturday. Where is my football? It is under my desk.     

第一届全国人民代表大会制定的《共同纲领》，是我国第一部社会主义类型的宪法。 （   ）