Suppose a state institutes a voucher program. Schools that have too many applicants use a lottery to randomly determine who can attend. The best approach to determining the effect of a voucher on student achievement is to compare the achievement of students ___________ to the achievement(s) of __________.

a - who won the lottery; the average student in the public school

b - in private schools; students in public schools

c - who won the lottery; students who lost the lottery

d - in schools with increased enrollment; students in schools with decreased enrollment