A:Sunday
B:Being Sunday
C:It to be Sunday
D:As it was Sunday
____
①用铁水铸造铁锅:____;
②钢锭变为钢水:____;
③河水结冰:____.
已知变量x,y满足{x≥1y≤2x-y≤0则x+y的最小值是( )