题目

At that time, what worried Zhang Yimou most was the weather,which we all know is evidently       anyone's control. A.above    B.beyond    C.under   D.over   答案：B1．已知一正三棱台上底边长为3，下底边长为6，高为3，则此三棱台体积为（　　）A．$\frac{{63\sqrt{3}}}{4}$B．$\frac{{21\sqrt{3}}}{4}$C．$\frac{{45\sqrt{3}}}{4}$D．$\frac{{15\sqrt{3}}}{4}$