21．Have you heard_____report? People with______good knowledge of engineering are in great need in the job market.

A．a; a

B．the; a

C．a; /

D．the;/

关于固定型药疹描述不正确的是：（）

A.皮疹愈合后留下灰黑色色素斑，约一周消退

B.皮疹好发于皮肤黏膜交界处

C.典型皮疹为圆形或类圆形的水肿性暗紫红色斑疹

D.皮疹常为一个

E.黏膜皱褶处糜烂时常感疼痛