What does the term "overpopulation" describe?
A)when many people want to live in a region, but the cost of housing there is too high for them to afford
B)when the people in a region have so many children that the adults living there are outnumbered
C)when a region is so crowded that no other people can physically fit in it
D)when there are not enough resources or facilities in a region to support the people living there