Hopefully I'm reading htis right...
The first chord is a G# dominant chord. A V7 chord in c# minor. G# B# D# F# Technically still a B#, although it's the same key as C natural. I was waiting for something else to say it.
That B# is very important. It leads up to the home base tonice note of C#. You can see that in beat 2.
That's why your teacher will be all over you if you miss it. It's not like playing another missed note. That's an important note and B natural isn't the same thing at all.
Don't forget the other B# on beat four. Beat four is the G#V7 again. The notes have just shifted. I see c# next in the bass. I bet there is a c# coming up soon that the B# resolves too. If you see the next B in ( ) 's or if the next B is marked natural, those are courtesy accidentals to remind the performer that that note has gone back to natural.