Giving up my job to go back to fulltime education was a big ________, but now I know it

was the best decision I have ever made. [ ]

A. project  

B. commitment

C. competition  

D. ambition

某水溶性营养素人体需要量与热能摄入量有关，为0.5mg/1000kcal，红细胞中谷胱甘肽还原酶活性与其水平有关。
该营养素可能为

A．维生素B₁
B．维生素B₆
C．维生素B₂
D．维生素A
E．以上都不是