老师，上次讲了两道DS，一道是邮票的，涉及到实际问题，且某一单价为0.15，数值特殊，第一个条件只能得出唯一解，所以选A。第二道也是门票问题，根据条件1不能得出唯一解，所以选C。这个题条件1和2的性质是一样的，其中任一条件与题干都可以列出两个方程，即X+Y=500和25X+15Y=10500，我想问老师根据这两个式子就可以确定出唯一解吗？感觉被这种类型的题搞蒙了 一、Joanna bought only $0.15 stamps and $0.29 stamps. How many $0.15 stamps did she buy? (1) She bought $4.40 worth of stamps. (2) She bought an equal number of $0.15 stamps and $0.29 stamps. 二、For a certain play performance, adults' tickets were sold for $12 each and children's tickets were sold for $8 each. How many children's tickets were sold for the performance? (1) The total revenue from the sale of adults' and children's tickets for the performance was $5,040. (2) The number of adults' tickets sold for the performance was 1/3 the total number of adults' and children's tickets sold for the performance.