Choose the word that has the underlined part different from others: out, sound, southern, surrounding

A. out /aʊt/

B. sound /saʊnd/

C. southen /ˈsʌð.ən/

D. surrounding /səˈraʊn.dɪŋ/

Explanation: Answer C is pronounced /ʌ/, the other answers are pronounced /aʊ/