Concept:The odd pair is the one that does not share a synonym or antonym relationship like the others.Explanation:Pair B (Happy : Ecstatic) is a synonym pair where the second word is a stronger form of the first.Pair D (Trail : Pathway) is a synonym pair with the same meaning.Pair A (Sad : Hopeful) is an antonym pair with opposite meanings.Pair C (High : Giant) shows neither synonym nor antonym relationship; the words are unrelated in meaning.Hence, High : Giant is the odd pair.Answer:C. High : Giant