Text-based stimulus: Answer-time timeline with a left region below 0 labeled invalid, a segment from 0 through 30 labeled quick, and a segment above 30 split by help_used True -> guided and help_used False -> independent. A response tracker receives answer_time_seconds and help_used. It must output "invalid" for negative time, "quick" for 0 through 30 seconds, "guided" when time is above 30 and help_used is True, and "independent" otherwise. Which structure is correct?