A．prepaid plans require a participation at most 3 or 4 years before starting college
B．children may start college 3 or 4 years earlier than at a normal age if they prepay tuition
C．college tuition 3 or 4 years later may not be so high as today's price of prepaid tuition
D．the younger a child to join the plan, the greater loss he/she will suffer at the age for college

A．combination
B．alliance
C．mixture
D．union