His initial broadcasting success as a young man was due at least as much to his considerable professional ------- as it was to his father's broadcasting connections.

A．(A) aplomb

B．(B) uncertainty

C．(C) hubris

D．(D) seniority

E．(E) nepotism

抗洪抢险中解放军战士穿的救生衣是用泡沫塑料（泡沫塑料的密度为0.3×10³kg/m³）制成的，使用时必须使人的头部露出水面（该部分体积约占人体总体积的1/10）才有效．如果救生衣的体积为2.4×10^-2m³，则使用该救生衣的解放军战士最大质量不得超过多少kg？（设人体的平均密度为1.06×10³kg/m³）