So difficult         it to work out the problem that I decided to ask Tom for advice. [ ]

A.I did find    

B.did I find

C.I have found      

D.have I found

在计算外商投资企业应纳税所得额时，除按规定可不留残值的固定资产外，计算折旧前固定资产的残值比例( )。

A．一般不低于原价的10%

B．一般不高于原价的10%

C．统一为原价的10%

D．一般不低于原价的5%