A white dwarf with a temperature of 10,000 K would fall into the spectral class A. This is because spectral class O is typically for stars with temperatures over 30,000 K, class B is for temperatures between about 10,000 K and 30,000 K, and class A is for temperatures around 7,500 K to 10,000 K. Given that the temperature is on the higher end for A, it aligns with that class. Therefore, the correct response is:
A