关系模式R(A1,A2,A3,A4,A5,A6,A7),给定函数依赖集合F={ A1→A2; A1→A3; A3→A4;A3→A5;A5→(A6,A7) } 则关于R,既保持依赖又无损连接地分解成第三范式,分解正确的是( )。
A.
r ={R1(A1,A2,A3, A4,A5) , R2(A5,A6,A7) }
B.
r ={R1(A1,A2, A3) , R2(A3,A4,A5) , R3(A5,A6,A7) }
C.
r ={R1(A1,A2, A3) , R2(A3,A4,A5,A6,A7) }