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

取某一巴比妥类药物约50mg，量试管中，加甲醛试液(或甲醛溶液)lml，加热煮沸，放冷，沿管壁缓慢加硫酸0.5ml，使成两层，置水浴中加热，界面显玫瑰红色。该药物应为

A．硫喷妥钠
B．苯巴比妥
C．司可巴比妥钠
D．异戊巴比妥
E．苯妥英钠