HELP QUICK PLS!! One of the spelling words is an exception to the rules, because it changes its internal spelling when the suffix is added (to reflect a change in pronunciation). What is the word?

acceptance
alliance
attendance
condense
condolence
conference
defense
existence
expense
experience
grievance
intelligence
intense
interference
nonsense
occurrence
perseverance
remembrance
repentance
resemblance
resistance
superintendence
vengeance
vigilance