Sentence 1: The best beach, one of the best on the entire island, is nearby, fronting a private vacation club.

Sentence 2: One of the best beaches is near a private vacation club.
Is this second sentence entailed by the first?

Answer: yes

Sentence 1: The lush river valley cuts deep into the heart of the mountains, with sheltered habitats for many birds and butterflies.

Sentence 2: The birds and butterflies would not be able to survive without sheltered habitats.
Is this second sentence entailed by the first?

Answer: it is not possible to tell

Sentence 1: It also marks Chinatown's southern boundary.

Sentence 2: It signals the edge of Chinatown.
Is this second sentence entailed by the first?

Answer:
yes