The correct answer is C.

Explanation: The vowel sound represented by the underlined letters "a" in "legal" is the same as the vowel sound in "mineral". In both cases, the vowel sound is a short, unstressed schwa sound /ə/.

- C. mineral: The first vowel sound is /ɪ/, which is closer to the schwa sound /ə/ in terms of vowel quality compared to the other options.

Other options:
- A. many: The vowel sound /æ/ is different from the schwa sound.
- B. margin: The vowel sound /ɑː/ is different from the schwa sound.
- D. rally: The vowel sound /æ/ is different from the schwa sound.

Thus, "mineral" is the word that has a vowel sound similar to the schwa sound in "legal."