The word ‘bought’ is transcribed /bc:t/ and it is the long vowel sound of /Ɔ/. The answer is A ‘roar’ /rc:r/ or /rc:r/ and it is the long vowel sound as ‘bought’ /bc:t/. the others have different vowel sounds like ‘plough’ /plau/, which has the diphthong /au/, ‘drought’ /draut/, also with the diphthong /au/ and ‘worse’ /wƷ:s/ which has a different sound.