We get _______ sometimes when we study in a group. But we can learn from each other in this way.

A．patient

B．silly

C．noisy

D．unfair

炉前冶炼HRB335钢，终点残锰0.05%，锰铁锰含量60%，锰的吸收率按90%计算，出钢量25t，问应加入锰铁多少kg？（该钢种锰含量中限为1.4%）