下列各组物质依次表示为a、b、c、d，图中箭头表示一步转化．满足如图所示转化关系的是

A．Na　Na₂O₂　NaOH　Na₂CO₃

B．S　SO₂　H₂SO₃　NaHSO₃

C．Cu　CuO　Cu(OH)₂　CuSO₄

D．Si　SiO₂　H₂SiO₃　Na₂SiO₃

An analyst does research about valuation models. With respect to equity valuation models, valuation working well for companies that do not have a high proportion of intangible or "off the books" assets and that do have a high proportion of current assets and current liabilities is best categorized as a(n):（）

A. multiplier model.

B. discounted cash flow model.

C. asset-based valuation model.