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 inconsistent with sentence (b)
D.sentence (a) contradicts sentence (b)

A.A.sentence
B.sentence
C.sentence
D.sentence

【参考答案】

B
如果a蕴含b，那么它们存在着如下的真值关系：当a为真时，b也一定为真；当b为假时，a为假。