题目

如图，AD⊥BC于D，那么图中以AD为高的三角形有   个． 答案：6 【知识讲解】∵AD⊥BC于D，而图中有一边在直线CB上，且以A为顶点的三角形有6个， ∴以AD为高的三角形有6个．故答案为：6With the word“PM2．5"_____ appearing in media reports，people pay greater attention to it and seek health tips for smoggy days．A．constantly B．instantly C．rarely D．directly