问题补充：
—is a boat ticket for children?
—How old is your child? It’s free for kids under three years old.
A. How long
B. How much
C. How often
D. How soon
答案：
A. How long
(答案→)B. How much
C. How often
D. How soon
解析：How long多长；How much多少钱；How often多久一次；How soon多久。根据下文，你的孩子多大了？三岁以下的孩子三块钱。可知上文提问的是价格，故选B，一张儿童船票多少钱？
