可以伴随着表的打开而自动打开的索引是______。

A．单一索引文件(ID

B．复合索引文件(CD

C．结构化复合索引文件

D．非结构化复合索引文件

In 1985 a company sold a brand of shoes to retailers for a fixed price per pair. In 1986 the number of pairs of the shoes that the company sold to retailers decreased by 20 percent, while the price per pair increased by 20 percent. If the company’s revenue from the sale of the shoes in 1986 was $3.0 million, what was the approximate revenue from the sale of the shoes in 1985 ？（）

A．$2.4 million

B．$2.9 million

C．$3.0 million

D．$3.1 million

E．$3.6 million