A few years ago the belief became general-orange juice and m

选a,主句是The belief became general.观念变得普遍
orange juice and milk should never be drunk at the same meal是用来补充主语The belief的
几年前,一个观念变的非常普遍,那就是橘子汁和牛奶不能在同一餐饭中饮用.
或者解释为几年前,橘子汁和牛奶不能在同一餐饮用的这么一个观念变的非常普遍.
so that是结果以至于,不符合上下文
and 虽然可以连接两个句子,但是不符合上下文,
such as 是举例子,因为前面the belief是单数的,所以没必要举例子.