用反证法求证：三角形的一个外角等于与它不相邻的两个内角的和．

Jan：I have new photos of my family, but they're not very good. This is my sister…
Mark：Where is she?  Is she at the library?
Jan：No, she's in the living room. She s doing her homework. And that s my brother.
Mark：Is he doing his homework, too? What's he eating?
Jan：He's watching a scary movie on TV and eating french fries.
This is a picture of my aunt and my mother.
Mark：Is that -your mother in the pool?
Jan：No, that's my aunt. My mother can't swim. And this is my mother and my aunt at the shop. They really like shopping and eating at the shop. Mark: Interesting photos.

在马赛人的社会里，拥有_______的数量越多的人越富有，社会声望也越高 (      )

糖受热会熔化成____，冷却后又会凝结成____。