设有关系模式R(X,Y,Z),F=X→Y,Y→Z,则R的候选键是______。
参考答案:X
Don’t believe what he said.His story is nothing.
A.based on
B.based of
C.based at
D.based about
只要产品批数多,就应该采用简化的分批法计算产品成本。