1. D
which只能指代物体,不能代指人：I,排除B；
that不能用于非限制性定语从句中,排除C；
非限制性定语从句中的关系代词who = 先行词I,所以后面是用am,排除A.
2. C
a bit of water = a little water,排除BD；
a little hungry 一点点渴；not a little thirsty = very thirsty 非常渴
3. B
定语从句的关系代词which不能指代人：those people,排除D；
关系代词who/whom/that = 先行词those peole,放入后面的定语从句中做find的宾语,即定语从句可以写成：
everybody will find those people hard to please.
= everybody will find it hard to please those people.
该句含有固定结构：感官动词find + 宾语those people + 宾语补足语 hard to please.
很明显,可以直接用hard to please做为宾语补足语.
而is/being不能用在此处,排除AC.