Translation:The donkeys were coming and going on the bridge.
Duo makes me crazy. Sometimes we are required to give the word by word translation. Other times we are required to give the English meaning. I know that in English "coming and going" is the accepted phrase, but put "going and coming" because that is the literal translation. I was marked wrong.
Is (The) donkeys required here. Previous sentences spring to mind, Birds have feathers. Owls are birds. Although les was in the french, not required for the english translation, is this sentence somehow different? Please bear in mind, I am already les/des challenged...
"The" is absolutely required for the English version of this sentence, because it's referring to specific donkeys. You can tell because 1) this sentence is in the past tense, so unless donkeys are extinct now, it cannot be describing a general characteristic of donkeys; 2) common sense should tell you that it is not a general characteristic of donkeys that they go back and forth over bridges.
We would usually use the article in English if talking about a specific group of donkeys... for example, the ones mentioned earlier in the narrative, or those waiting at the bridge etc. "Donkeys" without the article would mean donkeys in general, not a specific group of donkeys.