Crossword Clue:

Apply to participate in

AnswerCrossword Clue
OPT.. in (choose to participate)
OPTChoose to participate, with "in"
SEEOUTParticipate in to the end.
SATFailed to participate in, with "out"
SATFailed to participate in (with "out")
COUNTMEOUT"I refuse to participate in the census"