SAT OG语法题OG 8925.In the wild,pygmy chimpanzees are found onl

SAT OG语法题
OG 892
5.In the wild,pygmy chimpanzees are found only in an inaccessible region south of the Zaire River, since such is the case,very few are in captivity.
(A) since such is the case,very few are in captivity
(B) and very few are in captivity because of that
(C) no more than a few are in captivity as a result
(D) the number in captivity is very few for this reason
(E) and so no more than a few are in captivity
A和C的错误在哪里?还有正确答案的E“and”和“so‘在一起不算介词连用么?
“and”和“so‘在一起不算连词连用么？还是说“and so”一起作为一个连词，可是字典说“and so”是个副词……