设有关系R(A,B,C)和S(C,D)，与关系代数表达式πA，B，D(σR.C=S.C(R∞S))等价的SQL语句是( )

设有关系R(A,B,C)和S(C,D)，与关系代数表达式πA，B，D(σR.C=S.C(R∞S))等价的SQL语句是( )。

A.SELECT * FROM R，S WHERE R.C=S.C

B.SELECT A,B,D FROM R,S WHERE R.C=S.C

C.SELECT A,B,D FROM R,S WHERE R=S

D.SELECT A,B FROM R WHERE(SELECT D FROM S WHERE R.C=S.C

正确答案是B