动物患肺结核时，肺脏出现较大空洞的叩诊音是（）

A.浊音

B.清音

C.鼓音

D.半浊音

E.金属音

An investor does research about annual return and standard deviation of returns, and is considering the purchase of two securities issued by different companies operating in different industries. Each security has an expected annual return of 10 percent and an expected standard deviation of retums of 18 percent. Regardless of the weights selected, will a portfolio composed of the two securities most likeLy have an expected:()

A.A

B.B

C.C