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.
Domain Name Servers (DNS) are certainly necessary for easy access of resources across a network. The applicable options of the above are A and B - below are explanations as to why.
A: Computers generally are set to automatically obtain DNS information from the network they are connected to or can be pointed to a specific DNS server. This allows for records of where resources (network attach storage devices, other computers on local network, or even website server details) are located on a “master” kind of list so that the local machine’s host file does not have to be routinely updated to contain new addresses.
B: DNS, as explained partially by the answer to A, maintains a type-able or “human readable” domain name for the actual server’s IP address so we don’t have to memorize or keep a list of IPs for where we want to visit on the web (although, Google’s 8.8.8.8 IP address does make it easy). It shows an association between a name/domain name and an IP address so that we can enter something simple (Google.com) and the computer knows where to go (the server at IP address 8.8.8.8) so it can show you the content you want to see.
C: DNS would only simplify remote access if your were attempting LAN (Local Area Network) remote access of another computer on your network. DNS would not make it easier for remote access of a computer on the internet, as most DNS used in non-commercial settings are created and maintained by third-parties that will not put a specific record for one of your computers in it - not that you would want them to either, since it could lead to an open cyber attack.
D: Network throughput is a fancy phrase for network speed. It could be possible that different DNS servers could process requests faster than others, but it is not likely to increase network speed on the whole as navigating via IP or DNS records will be relatively the same speed.
3 Examples of mainframe computers
z900
System z9
System z10
