氟化硅(SiF4)是有毒的无色气体,可用于水泥和人造大理石的硬化剂等,制取氟化硅(SiF4)的化学方程式:2CaF2+H2SO4+SiO2CaSO4+SiF4↑+H2O,完成下列填空:
We have been in the school ______ three years ago and Mrs. Lee Has taught us English_______ three years.
如图,当输入x=﹣5,y=15时,图中程序运行后输出的结果为( )