Concept: The underlined letter "i" in "mitten" has the short vowel sound /ɪ/.Explanation: "Mitten" is pronounced /ˈmɪtən/, so the required vowel sound is /ɪ/."Knowledge" is pronounced /ˈnɒlɪdʒ/, and its final syllable "-ledge" contains the vowel sound /ɪ/."Firm" is /fɜːm/, "vice" is /vaɪs/, and "marine" is /məˈriːn/, none of which contain /ɪ/.Therefore, the correct option is the one that shares the same vowel sound.Answer: B. knowledge