古诗文阅读。
                                                                                                湖 上  
                                                                                               徐元杰
                                                                              花开红树乱莺啼，草长平湖白鹭飞。
                                                                              风日晴和人意好，夕阳箫鼓几船归。

下列现象中，属于特异性免疫的是（　　）