Which is a compound sentence? a. while my brother takes his dance class, i go to soccer practice

You did not include the rest of the question but with some googling i believe the answer you are looking for is:

A compound sentence is a sentence with more than one subject or predicate so... I painted my bedroom beige, but my sister painted her room blue is  the answer

where is the writing? (so i can answer)

faith or loyalty when pledged in a solemn agreement or undertaking.