Nature vs Nurture
(a) Having highly educated biological parents.According to results in a new study of Swedish data from Anders Björklund, Markus Jäntti, and Gary Solon , the answer is (a).
(b) Having highly educated adoptive parents.
The results in this paper seem broadly consistent with those of Dartmouth economist Bruce Sacerdote, who examines a completely different data set in which adopted children were assigned randomly to parents.
In both papers, nature is stronger than nurture for determining the educational attainment of adopted children, although both nature and nurture have some role. And in both papers, nature completely dominates over nurture for determining income. (See Table 3 in the Sacerdote paper and Table 3, column 6, in the Björklund et al. paper.)