作业精灵老师示例：
S1：Today we learn some rules about road safety.
S2：Rule 1：We must look for a zebra crossing, look at the traffic lights
and wait for the green man.
S3：Rule 2：We must wait on the pavement and look out for cars and bikes.
S4：Rule 3：We mustn't run or play football on the road.
S1：Follow these rules, and we can cross the road safely.
