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"Happens" is a form of "happen", an intransitive verb which is often translated as "suceder". Learn more about "happen" below.
happen(
hah
-
pihn
)An intransitive verb is one that does not require a direct object (e.g., The man sneezed.).
a. de casualidad (adverb)
If you happen to come by the office, we could get a coffee.Si de casualidad te pasas por la oficina, podemos tomar un café.