During a Visit in Central Park,Alan Values His First Hour

During a visit in Central Park,Alan values his first hour of walking at $10 and the second one at $7,Cooper values his first hour of walking at $6 and the second one at $1,and Emma values her first hour of walking at $20 and the second one at $15.Assuming that Alan,Cooper,and Emma are the only visitors in Central Park,what is true regarding the market demand for walks in Central Park?

A) The market demand is horizontal
B) Can be determined by horizontally adding up the individual demands
C) There is not enough information to determine the market demand
D) Can be determined by vertically adding up the individual demand
E) There isn't a demand for walks in Central Park