yes because you just did
you use (a) if the next word is not a vowel. you us (an) if the next word is a vowel.
Example sentence - His pessimism wore on all of us.
Writing this sentence will make us more frendlier.
There is chaos among us.
The production helped us produce
The boxer frighteningly barked at us.
Let us resolve our differences.
moM ....UM...MERcy on us.
The band director strongly encourages us to use dynamics.
There's nobody home but us chickens. Let us go free!
the majestic view of palace thrilled us
Let us rise and secure our country.