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MeerMeer
IDK what you're asking, but I'm guessing it's the grammar...

So the sentence you put in the question is: 

Mona. arrived on time, but. there was traffic. 
         ↑                               ↑
  (No Comma)           (No Period)
Leary
It means that Mona arrived on time, but there were lots of cars in front of her on her way, or there were lots of red lights