Final answer:
Sentence (a) and sentence (b) are not equivalent and do not entail each other. The correct answer is option D.
Step-by-step explanation:
The correct answer is D. None is correct.
In sentence (a), the subject 'they' implies that multiple people or entities own several buildings. In sentence (b), the possessive pronoun 'his' indicates that the ownership belongs to one person. Therefore, the statements in (a) and (b) are not equivalent, and neither entails the other.