The word "university" starts with the letter "u," which is a vowel. However, it is pronounced with a "ju" sound, which is a consonant sound.
The general rule for articles:
Since "university" is pronounced as "ju-ni-ver-si-ty" (starting with a consonant sound), the correct article is "a."
The correct sentence is:
"He will join a university."
Thus, the correct answer is (A) "a".