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.

原始凭证按照格式不同,分为（ ）。

A．外来凭证和自制凭证

B．通用凭证和专用凭证

C．一次凭证、累计凭证和汇总凭证

D．单项凭证和汇总凭证