Triangle

例句：

1. 1. The triangle is a shape with three sides and three angles.
   这个三角形有三个边和三个角。
2. 2.The triangle is the only shape that can be drawn on a piece of paper.
   三角形是唯一可以在纸上绘制的形状。
3. 3. The triangle is used to measure the length of a line.
   三角形用于测量线的长度。