Concept:The underlined letters in "destroy" together stand for the vowel sound /oi/, which is a diphthong.Explanation:The word "destroy" is pronounced /dɪˈstrɔɪ/.The target vowel sound is the one represented by the letters "oy", which is /ɔɪ/.Now check each option for its vowel sound:A. "poor" is pronounced /pʊə/ or /pɔː/, not /ɔɪ/.B. "boat" is pronounced /bəʊt/, containing the sound /əʊ/, not /ɔɪ/.C. "poise" is pronounced /poiz/, containing the same diphthong /ɔɪ/.D. "idea" is pronounced /aɪˈdɪə/, which has different vowel sounds.Only "poise" shares the exact vowel sound with "destroy".Answer:C. poise