I think a, or d, but I can't say for certain. I am sorry.
Explanation:
i think aliens do exsist
different birds have different to winter like some hibernate and some migrate
Examples of primary reinforcers include: food, drink and pleasure.
Secondary reinforcers include grades. Have a good day
The answer is C. Natural sources are limited. People tend to get their resources from the environment in order to live and survive. Because of the increasing number of human population, resources become scarce and there is not enough supply for consumption in the near future.
