There is______ old football under ______ bed. I like to play ______ football.     [ ]

A.an, the,  /    

B.the, the, the        

C.the, the , /        

D.an, a, the

当下述哪一条成立时，称X→Y为平凡的函数依赖

A．X包含于Y

B．Y包含于X

C．X∩Y＝

D．X∩Y＝