Option D is the answer because Digital Certificate is an entity that generates electronic and distributes them upon proving their identity sufficiently. In early days there was issues with people using the certificates that were not even issued by the organizations. Today it's a cryptographic technique which uses digital signatures and gives users a digital certificate that can be authenticated anytime online by any organization and is unique for every user having it.
Option A cannot be the answer because it has nothing to do with the identity of person but rather it is for specific fields.
Option B is not answer because it has no key and score matter to do with it.
Option C Web transactions has nothing to do with the certificates.
