[Pronunciation exercise]
• bus – boss
• color – collar
• cub – cob
• duck – dock
• dull – doll
• fund – fond
• hunk – honk
• hut – hot
• luck – lock
• nut – not
• rub – rob
• shut – shot
• stuck - stock

http://www.blairenglish.com/exercises/emails/exercises/how_to_disagree_in_email/how_to_disagree_in_email.html ...