若x≥0,y≥0,且x+y≤1,则z=x-y的最大值是( )。
1
_____ that he used to be a teacher. [ ]
A. It is said
B. It says
C. That is said
D. That says
银商通业务是指农业银行和()的系统对接。
A.证券交易所
B.期货交易所
C.大宗商品交易市场
D.担保机构