请教英语问题~~~

1.、---May I have a glass of beer ,please?
---Beer? Sorry ,there's _______left,but would you like some juice instead?
A.none B.something
C.no one D.nothing
为啥不选D，答案说 因为还有juice，不能用nothing，nothing就是什么也没有 ~能不能说详细些
2.One of the most important questions they had to consider was ____ of public health.
A. what B. this
C. that D. which
答案选that，可是quesions是复数，为啥还用that不用those
那么 nothing 表示什么都没有，不是指啤酒没有，又不是指可乐？

相关了解……