Answer:
D. Favorable.
Step-by-step explanation:
There is no doubt that the idea of living in such a benign climate was appealing. The islanders seemed to keep their vitality and live longer than Europeans.
Hence, the meaning of benign in this context is favorable. When a climate is referred to as being benign, it simply means that it is mild and favorable to the people found living in that geographical location.
Additionally, as a result of the favorable climate found in the island, the islanders keep their vitality and live longer than Europeans who are assumed to be poised with an unfavorable climate.