Answer:
b. the 25,000 adult American pine trees in the forest
Explanation:
Population refers to the total of all the subjects for which the study is done. The study here takes a sample of 250 trees approximately. But the conclusion of study will be applied on entire population under study which is 25,000 pine trees.
As the word population in a study refers to the total number on which the conclusion will be applied. as in the given case if all the samples are above the height of 60 feet, it will be concluded that the entire population of about 25,000 pine trees is above 60 feet.