Concept:The target sound is the central vowel /ɜː/, which appears in the word "perk".
Explanation:The question expects us to find the word whose underlined letters produce the same vowel sound as in "perk".
The sound /ɜː/ is a long, mid-central vowel, often spelled as "er", "ir", or "ur".
Now check each option carefully.
A. "batter": pronounced /ˈbætə/, the letter "a" gives /æ/, not /ɜː/.
B. "barter": pronounced /ˈbɑːtə/, the letters "ar" give /ɑː/, not /ɜː/.
C. "perk": pronounced /pɜːk/, the letters "er" give the exact vowel /ɜː/.
D. "martyr": pronounced /ˈmɑːtə/, the stressed "ar" gives /ɑː/, not /ɜː/.
Therefore, only "perk" shares the required vowel sound.
Answer:C. perk