有三名同学,一起去找老师问题目。老师三言两语道破了问题的关键,然后话锋顺势一转,指出这道题目有三种变化,并让学生拿笔在纸上算一算。老师桌上有厚厚的一叠纸,还分别拿出了三支笔:一支钢笔、一支圆珠笔、一支铅笔。学生甲说:“我要圆珠笔。” There are three classmates, go to the teacher to ask questions. The teacher repeated the crux of the problem in a few words, and then took the opportunity to point out that there were three changes to this topic and that students should take a pen to calculate on paper. There was a thick pile of paper on the teacher’s desk with three separate pens: a pen, a ballpoint pen and a pencil. Student A said: “I want a ballpoint pen.”