Dear students, "u" is a semi-vowel;this means that sometimes it behaves as a vowel like in "umbrella","ultimatum","underproduction"etc when an"an" is necessary.Other times it behaves like a consonant as in "university","union","unique" when an "a" is needed.Practice will help!
Kalli is absolutely right and so is of course,BobK.
Not only does that happen to U but to E too...ex: a European country, an abbreviations like an MP..
The answer is A because A or An depends on pronunciation. If any word's pronunciation starts with "a" like umbrella we put "an". otherwise we use "a"..
read the word and listen to the difference in the sounds of the words such as (YU) as in uniform or (A) as in up.