保护层施工中，金属保护层应紧贴在绝热层或防潮层上，立式设备应自下而上逐块安装，环缝和

He is the only one of the students who __________a winner of scholarship for three years.

A．is

B．are

C．have been

D．has been

______ 就是利用图解的方式来说明在某个过程中各要素之间是如何相互联系的。 ( )

A．流程图

B．网络关系图

C．系统结构图

D．模型图

--Where have you been?

--I_____in the heavy traffic. Otherwise I_____ here earlier.

A．got stuck; would have come

B．got stuck; was

C．have got stuck; would have come

D．had got stuck; would come

用曼宁公式作高水延长时，曼宁公式中的S是实测的（）。

A、水面横比降

B、水面纵比降

C、河床糙率

D、河床坡降

设f(x)在[1，+∞)上有连续的二阶导数，f(1)=0，f’(1)=1，且二元函数z=(x²+y²)f(x²+y²)满足

，求f(x)在[1，+∞)的最大值．