英语定语从句问题，求解答？1.—Here is so difficult a problem____none of us

英语定语从句问题，求解答？
1.—Here is so difficult a problem____none of us can solve.
A which B that C as D what
So….as与so….that在这里怎么区分使用呢？

2.--I was born in New Orleans, Louisiana, a city _______name will
create a Picture of beautiful trees and green grass in our mind.
A . which B . of which C. that D. whose
答案是whose，为什么不用of which
3.—He is the same man____she has seen
A whom B that C which D who
答案是that。这句话怎么翻译？为什么不用whom或who?