Not enough information to answer the question. Is this multiple choice? What's the context?
Answer:
A. Less than 50% had had sexual intercourse.
Answer:
Natural factors of population change can't be swayed by humans. So for an example of a natural factor take an Earthquake. As of right now we can only predict when Earthquakes will. Inevitably some things will still get damaged and that just can't be helped. An Artificial factor for population change is something specifically made by humans. For an example take a genocide. If some guy decides he wants to go on a killing spree, well all I can say is that is Definitely not natural. Hope that helped.
Self-care encourages you to maintain a healthy relationship with yourself so that you can transmit the good feelings to others. You cannot give to others what you don't have yourself. While some may misconstrue self-care as selfish, it's far from that.
