片段一(在情境中提出问题):师:用什么方法可以测量出一元硬币或五角硬币的圆周长。生1:我把一元硬币放在直尺上滚动一周,量出这枚硬币的周长大约是8cm。生2:我在5角硬币的圆周上做了个记号,然后放在直尺上滚动了一周,量出了这枚硬币的周长大约是6.3cm。师:你们俩都用滚动法量出 Fragment 1 (asking questions in context): Teacher: In what ways can I measure the circumference of a dollar coin or a five-pointed coin? Students 1: I put a dollar coin on the ruler to scroll a week, measuring the circumference of this coin is about 8cm. Student 2: I made a mark on the circumference of a 5-cent coin and then rolled it on the ruler for a week, measuring the circumference of this coin about 6.3cm. Teacher: You both measure it by rolling