Concept:The underlined letters oo in the word mood produce the long vowel sound /uː/.Explanation:The word mood is pronounced /muːd/.Its vowel sound is the long /uː/, like in the word soon.Now check each option:A. took → /tʊk/ has the short vowel /ʊ/.B. look → /lʊk/ also has the short vowel /ʊ/.C. moon → /muːn/ has the long vowel /uː/, which is the same as in mood.D. mode → /moʊd/ has the diphthong /oʊ/.Only moon shares the same vowel sound /uː/.Answer:C. moon