双二硫腙光度法测Pb，选用波长为（）。

A.510nm 

B.440nm 

C.660nm 

D.540nm

Somebody bought some pencils and rubbers in a shop. What's the price for each pencil
(1)he paid 215 cents for 2 pencils and 3rubbers
(2)he should have bought 8 pencils and12 rubbers if he paid 860 cents.

A．条件(1)充分，但条件(2)不充分．

B．条件(2)充分，但条件(1)不充分．

C．条件(1)和(2)单独都不充分，但条件(1)和条件(2)联合起来充分．

D．条件(1)充分，条件(2)也充分．

E．(E) 条件(1)和条件(2)单独都不充分，条件(1)和条件(2)联合起来也不充分．