设有关系R(A,B,C),与SQL语句selectdistinct Afrom R where C=36等价的关系代数表达式是

设有关系R(A，B，C)，与SQL语句select distinct A from R where C=36等价的关系代数表达式是

A．πA(σC=36(R))

B．σC=36(πA (R))

C．σC=36(πA,B (R))

D．πA,B(σC=36(R))