光华公司现金收支状况比较稳定，全年的现金需要量为600万元，每次转换有价证券的固定成本为100元，有价证券的年利率为12%。其年转换成本是( )元。

A．6000

B．8000

C．9000

D．10000

Advertisement: We at Vesuvius Vacuums always give our customers what they deserve, and they deserve the very best. That’s why we use only SuperTec air filters.
Which of the following, if true, would most undermine the argument expressed in the advertisement ？（）

A. In a test of three leading air filters, the SuperTec air filter performed at the same level as one of the filters and at a higher level than the other.

B. The SuperTec air filter is the only kind of air filter that will fit in the model of vacuum sold by Vesuvius Vacuums.

C. In a national study by a prominent consumer group, Vesuvius Vacuums gained a "superior" rating for product quality.

D. The customers of Vesuvius Vacuums have expressed no preferences concerning the type of air filter used in the product.

E. The specific air filter used in a given vacuum makes only a small difference in the long-term performance of that vacuum.