Some Fear a Serious Deterioration of the Biological Quality of the Human

Some fear a serious deterioration of the biological quality of the human population because:

A) intelligent individuals will choose careers over family leaving the less advantaged and less educated to bear the majority of children.
B) the birth rates are declining meaning the chances of healthy offspring is decreasing.
C) the birth rates are increasing meaning the available talent of a society is being spread more thinly.
D) of the limited interchange between people with different enough genes.