阅读下面短文，按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用括号中词语的正确形式填空。每空不多于3个单词。

    Mary has ____ cousins. They are Betty, Peter, Bill and Ann.

    Mary is ____ (old) of five. Betty is thirteen years old. She is two years younger ____Mary and one year older than Peter. Ann is the youngest and she is naughty(淘气的). When her mother asks her ____（wash） hands, he never washes them ____ (careful). She only puts her hands in the water ____ a few seconds(秒) and took them out again. Betty and Peter are good at ____(run). They also like playing basketball. Peter plays ____(good) than Betty. Bill and Mary study in ____ same school. They study in No.1 School. Both of them always get good ____ (grade).

增加：在缺词处加一个漏字符号（∧），并在右边横线上写出该加的词。

删除：把多余的词用斜线（\）划掉，并在右边横线上写出该词，也用斜线划掉。

修改：在错的词下划一横线，并在右边横线上写出修改后的词。

甲、乙两人从相距15km的两地同时出发，相向而行，甲的速度为3km／h，乙的速度为2km／h，甲带一条狗，同甲一起出发，狗的速度4km／h，狗碰到乙后又往甲方向走，碰到甲后它又往乙方向走，这样持续下去，直到甲乙相遇时，这条狗一共走了____km。