It has been announced recently that all the schools________ not have the students attend school if the

students have high temperatures.[ ]

A. need  

B. shall  

C. could  

D. ought to

在总压强为3×10⁵帕下，将氮．氢混和气体通入合成塔，反应达平衡时，按的体积百分含量为20%，平衡时压强为[ ]

A．1×10⁷帕

B．2．5×10⁷帕

C．5×10⁷帕

D．10×10⁷帕