When the truth of sentence(a)guarantees the truth of sentence(b)and the falsity of sentence(b) guarantees the falsity of sentence(a)，we can say that_________．

A.sentence(a)presupposes sentence(b)

B.sentence(a)entails sentence(b)

C.sentence(a)is synonymous with sentence(b)

D.sentence(a)contradicts sentence(b)