X线有物理特性、化学特性和生物特性，下列属于化学特性的是哪项（）

A.穿透作用

B.荧光作用

C.感光作用

D.干涉与衍射、反射与折射作用

E.电离作用

A portfolio is equally invested in Stock A, with an expected return of 6 percent, and Stock B, with an expected return of 10 percent, and a risk-free asset with a return of 5 percent. The expected return on the portfolio is:（）

A. 7.4%.

B. 8.0%.

C. 7.0%.