could you buy drinks___snacks?为什么用and不用or呢

could you buy drinks___snacks?为什么用and不用or呢 这里为什么用could呢?You can buy as much as spaghetti as you could. nothing to sell and nothing to buy为什么不用or or和and的区别or用于疑问句,和否定句,但为什么这句:Could you buy some drinks and f could you come with me,please?这里为什么用could 而不用can 呢? could you please buy（ ）snacks（ ）drinks?填 some and还是any or Is to rush and run to you 中为什么用and不用or Nobody could ever replace you为什么用could不用can could you please buy _____drinks and snacks? Study hard ,or you will fail in the exam or为什么不用and where did you buy yesterday 为什么buy不用过去式 I guess I could come over.为什么用could不用can呢