经济净现值是指用()将项目计算期内各年的净效益流量折算到建设期初的现值之和。

A.名义利率

B.行业基准折现率

C.社会折现率

D.实际利率

He has poor eyesight _______computer work

A．because too many

B．because too many

C．because of too much

D．because of much too