That has happened quite a few times now in the slow part of many of the sections. the "una" is pronounced as "eena". When you hear that in the slow section, there will be a good chance that it will be "una"
Good tip. It certainly sounded like eena to me. This is good practice, though, because as you may well know, when you go to a Spanish speaking area and practice your Spanish, the replies you get will have regional accents which will change the textbook-pronounced words considerably. These pronunciations become additions to your vocabulary.
somos is from the verb "ser". When speaking of location, the verb "estar" is used.
while I am no expert, I believe it is because ciudad is feminine, and the preceding 'a' in 'a city' needs to indicate that. So it would be una ciudad, a city. Or, un pueblo for a town. Pueblo is a masculine noun, therefore the 'un'. I know, figuring the gender is sometimes tough, buy so far as I can tell, if it ends in an 'o' it is masculine, an 'a' indicates feminine, and some others, we just need to remember.
Is 'cuidad' masculine or feminine? I can never remember... This question uses 'una' which is feminine. Is there any circumstance when 'cuidad' is 'el cuidad'?
feminine, as is the case with most words that end in "-dad." It will never take "el"