Final answer:
The best answer to complete the sentence 'Vamos a mi cumpleaños.' is 'celebrar'.
Step-by-step explanation:
The best answer to complete the sentence 'Vamos a mi cumpleaños.' is 'celebrar'. In Spanish, the word 'celebrar' means 'to celebrate', so the correct sentence would be 'Vamos a celebrar mi cumpleaños' which translates to 'We are going to celebrate my birthday'.
Learn more about Completing a sentence in Spanish