选择题
2015 AMC 8 Problem 20: Sock Prices
Ralph bought 12 pairs of socks for a total of $24. Some socks cost $1 a pair, some cost $3 a pair, and some cost $4 a pair. If he bought at least one pair of each type, how many pairs of $1 socks did Ralph buy?
2015 AMC 8 第 20 题：股票价格
拉尔夫买了 12 双袜子，总共 24 美元。有些袜子售价 1 美元一双，有些袜子售价 3 美元一双，有些袜子售价 4 美元一双。如果他每种类型至少买一双，拉尔夫买了多少双 1 美元的袜子
A.
4
B.
5
C.
6
D.
7
E.
8