题型:问答题 简答题 It is high time we ______ awareness of environmental protection.A.promotedB.would promoteC.shall promoteD.had promoted 查看答案
题型:问答题 简答题 设U为所有属性,X、Y、Z为属性集,Z=U-X-Y,下面关于多值依赖的叙述中,哪一条是正确的A.设XYWU,若X→→Y在R(W)上成立,则X→→Y在R(U)上成立B.若X→→Y在R(U)上成立,且YY,则X→→Y在R(U)上成立C.若X→→Y,则X→→ZD.若X→→X,则X→N 查看答案