The mandatory training for those who handle dangerous goods must be renewed every:

Answer: A — Thirty-six months

The mandatory training for those who handle dangerous goods must be renewed every thirty-six months. This is because the training needs to be updated every three years to ensure that individuals handling dangerous goods are aware of any new regulations, safety procedures, or best practices. Option B, twenty-four months, is too frequent and may become a burden for individuals to continuously renew their training. Option C, twelve months, is too infrequent and may not allow individuals to keep up with changing regulations. Option D, forty-eight months, is also too infrequent and may not provide enough practice or refreshment of knowledge for handling dangerous goods. Overall, the most appropriate and safest option is A, thirty-six months, to ensure that individuals are properly trained and aware of any changes in regulations.