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)