患者，女，24岁。长期口角糜烂，最可能缺乏的营养素是

A．维生素B1 

B．维生素B2 

C．维生素B6 

D．维生素B12 

E．维生素PP

The job is         to me because I have little experience, however, it is also        .[ ]

A. challenging; rewarding

B. challenged; rewarded

C. challenging; rewarded

D. challenged; rewarding