When workers agree to forego leisure to undertake labor and receive wages, the term that is applied in labor supply economics is the:（）

A. substitution effect.

B. income effect.

C. marginal rate of substitution.

脊椎退行性变的病理改变中，包括哪项（）

A.椎间盘退行性变

B.椎间关节退行性变

C.韧带退行性变

D.脊椎骨骼改变

E.脊椎结核、肿瘤病变