单项选择题A.{(Sno, Sname, Cno, Tname, Taddr), (Sno, Sname, Cno, Cname, Grade) } ∈ 2NFB.{(Sno, Shame), (Sno, Cno, Grade, Tname, Taddr), (Cno, Cname)}∈ 2NFC.{(Sno, Sname), (Sno, Cno, Grade), (Tname, Taddr), (Cno, Cname) } ∈ 3NFD.{(Sno, Sname), (Sno, Cno, Grade), (Tname, Taddr), (Tname, Cno), (Cno, Cname)}∈3NF
A.{(Sno, Sname, Cno, Tname, Taddr), (Sno, Sname, Cno, Cname, Grade) } ∈ 2NF
B.{(Sno, Shame), (Sno, Cno, Grade, Tname, Taddr), (Cno, Cname)}∈ 2NF
C.{(Sno, Sname), (Sno, Cno, Grade), (Tname, Taddr), (Cno, Cname) } ∈ 3NF
D.{(Sno, Sname), (Sno, Cno, Grade), (Tname, Taddr), (Tname, Cno), (Cno, Cname)}∈3NF