Gus Hayden, CFA, has developed a mutual fund selection product based on historical information from 2000-2010 period and performs a hypothesis test about performances of different styles. In order to minimize the probability of both Type Ⅰ and Type Ⅱ error, Hayden should increase the:（）

A. the power of a test.

B. level of significance.

C. sample size.

在关系运算中，查找满足一定条件的元组的运算称之为( )。

A．复制

B．选择

C．投影

D．连接