Check each option against the word voracious.
Option A: Tenacious means persistent or firm, not about appetite. Wrong.
Option B: Truthful means honest. It has nothing to do with hunger. Wrong.
Option C: Spacious means roomy or large in area, again unrelated to appetite. Wrong.
Option D: Ravenous means extremely hungry or greedy for food, which matches voracious exactly.
By elimination, the correct answer is Ravenous, option D.