The old man, _______ abroad for twenty years, is on the way back to his motherland.

A．to work　

B．working 

C．to have worked

D．having worked

工程建设定额按( )分类方式，可以分为施工定额、预算定额、概算定额、投资估算指标等。

A．定额反映的生产要素消耗内容

B．定额的编制程序和用途

C．投资的费用性质

D．专业性质