If a person's certification is invalid, what must they fulfill to regain their certification?

To regain their certification, a person must fulfill all previous requirements associated with that certification. This means that the individual needs to meet the standards that were originally set for obtaining and maintaining the certification to ensure they are fully compliant with the regulations and expectations. This typically involves demonstrating that they are competent and knowledgeable in their field, which can include fulfilling continuing education requirements, passing any necessary exams, or completing any stipulated training.

Regarding the other choices, while completing a new application or taking necessary exams may seem relevant, they are not sufficient on their own. Letters of recommendation may be beneficial in other contexts but are not a primary requirement to regain certification. Therefore, fulfilling all previous requirements is the comprehensive approach that encompasses all activities needed to restore certification status.