Which of the following is the act of proving to a customer that software developers are trained on secure coding?

Attestation is the act of providing proof or evidence that a certain claim is true. In this context, it means proving to a customer that software developers have indeed received training in secure coding practices. This often involves providing documentation, certifications, or audit reports. Assurance refers to the overall confidence in the security of a system or process, but it's not the specific act of proving a claim. A contract is a formal agreement, not the act of proving a specific training. Due diligence is the reasonable steps taken by a person or organization to avoid harm to other persons or their property, which is a broader concept than proving specific training.