It is probably easier for teachers than for students to appreciate the reasons why learning English seems to become increasingly difficult once the basic structures and patterns of the language have been understood．

治疗月经后期虚寒证，应首选

A．《金匮要略》温经汤
B．《妇人大全良方》温经汤
C．大补元煎
D．乌药汤
E．小建中汤