Answer:
-Fue entonces que la vi llorando.
-Yo esperaba el autobús y entonces llegó él y me saludó.
-Por aquel entonces, yo aún no estudiaba en la universidad.
Step-by-step explanation:
The adverbial word "entonces" have a similar meaning to the words "so", "then", "at that time" in English.
So the sentences above can be translated like this ones:
-It was then that I saw her crying.
-I was waiting for the bus and then, he arrived and greeted me.
-At that time, I didn't study at university.