如图甲所示，在一根横跨河流两岸的硬塑料管内穿有三根完全相同的导线．为了辨别哪两个线头为同一根导线的两端，工人师傅用图6乙所示的“测通器”来进行测试．他首先将A和B连接起来，然后将“测通器”的m连接在D上，将n连接在F上，发现此时小灯泡发光…．工人师傅据此可知____ 为同一根导线的两端，接着他把A与C相连，m接在E上，用n去接触F，若灯泡不发光，则____ 为同一根导线的两端，____ 为另一根导线的两端．

在日常生活中，能够说明大地是球形的自然现象是（　　）

   This boy is Peter Smith. His1 name is Peter. His2 name is Smith. This is3 school. His school4number is 20048567. His teacher is Miss White. Miss White 5a good teacher. Li Min is a Chinese boy. Li Min is his good 6 at school. Look!7 a pencil sharpener. Is the pencil sharpener 8? I9know. Let's10 Li Min at 495-6548.

“天无三日晴，地无三里平”指的是（　　）