All the baobab trees that were selected in this habitat
All the baobab trees that were years old in this habitat
All the baobab trees that were years old in South Africa
All the baobab trees that were years old in this habitat
Explanation
Correct answer: D.
Choice D is correct. When a study uses a randomly selected sample, the largest group to which the results of the study can be applied is the population from which the sample was selected. It's given that the scientist randomly selected the trees from the baobab trees in a certain habitat that were years old. Therefore, the largest group to which the results of this study can be applied is all the baobab trees that were years old in this habitat.
Why the other choices are wrong
Choice A
Choice A is incorrect. Since the sample was randomly selected from a population, the results can be applied to a larger group than the sample.
Choice B
Choice B is incorrect. The sample was selected from a population of baobab trees that were years old, not years old.
Choice C
Choice C is incorrect. The sample was selected from a certain tree habitat in South Africa, not from all the baobab trees that were years old in South Africa.