They have more choices as to what they buy and from whom.

1 翻译：就买什么和从谁那儿买东西,他们有更多的选择.
2 as to == about / concerning ：有关-- - ,关於- -.
3 from是介词,所以,from + 代词宾格.
5 from whom they buy == who / whom they buy from == who / whom they buy from.是不是from后面必须用宾格whom？- 是不是from后面必须用宾格whom？- 是的。