Certificate chaining is used to delegate authority to subordinate certificate authorities. So, that is not the correct answer. Certificate pinning is a technique used to prevent changes in the valid certificate for a domain, which is another incorrect answer. Certificate stapling attaches an OCSP validation to the digital certificate, making it our correct answer. Certificate stapling also saves the client and server the time of repeatedly querying the OCSP server for certificate validity. That last choice, certificate attachment, is just a made-up term and it’s not a valid technique.