____ （有时）I play sports after class .

①b²﹣4ac＞0；

②x=x₀是方程ax²+bx+c=y₀的解；

③x₁＜x₀＜x₂

④a（x₀﹣x₁）（x₀﹣x₂）＜0；

⑤x₀＜x₁或x₀＞x₂，

其中正确的有（   ）

对流层大气的直接热源是(    　)

阅读下面这首古诗，回答两题。
                                                                                                                                              客发笤溪^①
                                                                                                                                                 清 叶燮
                                                                                                                            客心如水水如愁，容易归帆赴疾流。
                                                                                                                            忽讶船窗送吴语，故山月已挂船头。   
      【注】①笤溪是流经诗人家乡吴兴的一条河流。