2.对谓词公式(ꓯx )(A(x)→B(x,y))∧C(x,y)换名(换元)正确的是
A ( ꓯz) (A(z)→B(z,y))∧C(z,y)
B (ꓯ z) (A(z)→B(z,y))∧C(x,y)
C (ꓯ y)(A(y)→B(y,y))∧C(x,y)
D (ꓯx )(A(x)→B(x,z))∧C(x,z)