Answer:
I met __a___ European.
We sat under __the__ Eucalyptas.
There is ___a__ euphemism in the line.
___The___ English are brave.
This was ___the___ worst experience.
This is ___a__ useless thing.
Is not he __an__ honest man?
Explanation:
So in English, there are some exceptions to when you use "an" before words that start with vowels, and also some words that start with consonats and use "an." These might be tricky, but the best way to figure them out is to say them out loud. For example, if you said the first one out loud and you used "an" it would sound really weird. The best tip for trying to figure out grammar in English is to just sound the sentence or question out.