in the exercise there's a word used "sûrement" as "probably",
however here it says it means "certainly":
http://dictionnaire.sensagent.leparisien.fr/SUREMENT/fr-fr/
and here seems to be meaning both:
https://context.reverso.net/translation/french-english/s%C3%BBrement?utm_source=reversoweb&utm_medium=contextresults&utm_campaign=resultpage