Translation:Ik nam de gelegenheid om te drinken.
Is "om" mandatory in this sentence?
No, not in this one. ;)
"Ik nam de mogelijkheid om te drinken" was not accepted, why? I also reported it, but I would like to know the difference between mogelijkheid and gelegenheid. :)
Think of "mogelijkheid" as "possibility", and "gelegenheid" as "opportunity".