A.A=C C=B B=A B.A=A+B B=A-B A=A-B C.A=B B=A D.A=(A+B)/2 B=(A-B)/2
A."數(shù)據(jù)庫"+"系統(tǒng)" B."數(shù)據(jù)庫 "+"系統(tǒng)" C."數(shù)據(jù)庫"-"系統(tǒng)" D."數(shù)據(jù)庫"-" 系統(tǒng)"
A.3 B.1 C.-3 D.-1