At the party... How do I say that?

منذ شهرين

Greetings from Berlin, everyone! 😘 Now, to all of you dears learning German, I have a question:
When I am at the party, I say:

a) Ich bin bei der Party

b) Ich bin an der Party

c) Ich bin auf der Party

d) Ich bin zu der Party

For the answer as well as more tips such as this one, book a trial lesson with me! Let's have some fun! 😊