Problem: The ideal way to identify the effects of immigration on the health of immigrants' children is to:
a. Survey immigrants' children and compare main health indicators to the health of locals' children at the destination country
b. Survey immigrants' children and compare main health indicators with the health of other immigrants' children
c. Use a lottery to determine families which immigrate and then compare main health indicators of the immigrants' children with the children of those who did not get the immigration lottery
d. Study the average health of immigrants' children across time