单项选择题
A.(∀x)(A(x)∧B(x))B.┐(∀x)(A(x)→B(x))C.(∃x)(A(x)∧B(x))D.┐(∃x)(A(x)∧┐B(x))
A.5B.10C.9D.12
A.10B.20C.30D.5