Final answer:
A nursing assistant certification typically needs to be renewed every two years, but this can vary by state or certifying body.
Step-by-step explanation:
The certification for a nursing assistant must be renewed periodically to ensure that the assistant remains knowledgeable about best practices and complies with regulations. However, the renewal period can vary by state or certifying body.
Typically, a certification for a nursing assistant needs to be renewed every two years, which makes option b) the most common answer. Nonetheless, it's important for nursing assistants to check the specific requirements for their state or employer to confirm the exact renewal period required for their certification.