下列函数中，是二次函数的是（　　）

    One day, in an English class, the students are doing their lessons. Their teacher, a young woman, is very happy. She sings with them and then she goes to the blackboard and writes “SMILES” on it.
    “This is the longest word in English,” she says to the class.
    A girl stands up and says, “It has only six letters. How can it be the longest word in English?”
    The teacher smiles and says, “Oh, look! There is a mile (英里) between the first letter and the last one.”

互联网平台释放了不少正能量，比如突发灾难中的守望相助、公益行动中的慷慨解囊、网络问政中的良性互动、微博反腐中的穷追不舍等。同时也必须正视网络空间中的各种乱象，如“水军”“推手”制造话题，黑客、病毒无孔不入，虚假信息泛滥成灾，各种违法行为屡禁不绝等等。因此，互联网文化建设应当（    ）

①加强文化市场管理，净化网络社会文化环境

②加强思想道德建设，全面提高公民道德素质

③大力发展文化事业，全方位提升文化竞争力

④积极推广信息技术，促进传媒的商业化发展