bivati

1. (of events, phenomena) to happen; to occur
   Tako to biva kad ne slušaš roditelje. — That's what happens when you don't listen to your parents.
   Kod nas zimi biva i do minus dvadeset. — Here it sometimes gets down to minus twenty in winter.
2. (of gradual change) to become; to grow
   Svakim danom biva sve toplije. — It's getting warmer every day.
   Situacija biva sve komplikovanija. — The situation is getting more and more complicated.
3. (of a state, situation) to be on repeated occasions
   Često je bivao sam. — He was often alone.

In Serbia, as in Croatia, it can be used as a passive auxiliary (bivao je kažnjavan), usually in written and formal style.