如下表所示，X={butter, cheese}，Y={beer}，则置信度confidence(X→Y)=（）。交易号（TID）商品（Items）1beer, diaper, nuts2beer, biscuit, diaper3bread, butter, cheese4beer, cheese, diaper, nuts5beer, butter, cheese, nuts

A.1/2

B.1/3

C.1/4

D.2/5

正确答案：1/2