设A(x)：x是金属，B(x)：x是金子，则命题“有的金属是金子”可符号化为（ ）．

(x)(A(x)∧B(x))     

┐("x)(A(x) →B(x)) 

(x)(A(x)∧B(x))   

┐(x)(A(x)∧┐B(x))