Final answer:
Sentence A best summarizes the effect Sea Turtles Inc. has had by indicating a significant increase in Kemp's ridley sea turtle nests due to their conservation efforts.
Step-by-step explanation:
The sentence that best summarizes the effect Sea Turtles Inc. has had on the Kemp's ridley sea turtles is: "There are now about 11,000 which make some 15,000 nests a year—the animals make multiple nests in alternating years—making them a rare marine conservation success story." This sentence highlights the positive impact that conservation efforts have had on the sea turtle population. The increase in the number of nests signifies a successful recovery, emphasizing the significance of protection measures.