酸枣仁汤中配伍川芎的主要用意是（）

A.祛瘀血，止疼痛

B.行气滞，化瘀血

C.调肝血，疏肝气

D.祛风邪，止头痛

E.祛风邪，止痹痛

Some Maths problems in this book are       difficult for the students        work out.[ ]

A. so, that

B. not, but

C. such, that

D. too, to