Concept:The phonetic symbol /a:/ represents a long vowel sound, commonly found in words with "ar" spelling.Explanation:The vowel in "pat" is the short sound /æ/.The vowel in "angry" is also the short sound /æ/.The vowel in "lark" is the long sound /a:/.The vowel in "prank" is also the short sound /æ/.So, only "lark" contains the required sound.Answer:C. lark