（ ）dark it is,she still went to the classroom.

（ ）dark it is,she still went to the classroom.
a though b as c however d but
答案是c
汗颜..
我忘记问了 为什么选c
让不行状语的连词 不也可以用a么 用cdscdma 的观点排除a 是正确的么？