SCADA stands for supervisory control and data acquisition. It refers to industrial control systems (ICS): computer systems that monitor and control industrial, infrastructure, or facility-based processes. It is a category of software application program for process control, the gathering of data in real time from remote locations in order to control equipment and conditions. SCADA is used in power plants as well as in oil and gas refining, telecommunications, transportation, and water and waste control.
SCADA systems include hardware and software components. Hardware gathers and feeds data into a computer system that has SCADA software installed. The computer then processes this data and presents it in a timely manner. This system also records and logs all events into a file stored on a hard disk or sends them to a printer. It warns when conditions become hazardous by sounding alarms.

Certificate Revocation List (CRL) is one of the two common methods when using a public key infrastructure for maintaining access to servers in a network. Online Certificate Status Protocol (OCSP), a newer method, has superseded CRL in some cases.
The CRL is a list of subscribers paired with digital certificate status. The list enumerates revoked certificates along with the reason for revocation. The dates of certificate issue, and the entities that issued them, are also included. The main limitation of CRL is the fact that updates must be frequently downloaded to keep the list current OCSP overcomes this limitation by checking certificate status in real time. The OCSP allows the authenticity of a certificate to be immediately verified.

A smartphone is a mobile phone that offers more advanced computing ability and connectivity than a contemporary basic feature phone. A smartphone is a mobile phone with advanced PC like capabilities. Blackberry and iPhone are the two most popular brands of smartphones. It allows the user to install and run more advanced applications based on a specific platform.

Answer options C and B are incorrect. An IP phone uses Voice over IP technologies, allowing telephone calls to be made over an IP network such as the Internet instead of the ordinary PSTN system. Calls can traverse the Internet, or a private IP Network such as that of a company. The phones use control protocols such as Session Initiation Protocol, Skinny Client Control Protocol, or one of the various proprietary protocols such as Skype. IP phones can be simple software-based Softphones or purpose-built hardware devices that appear much like an ordinary telephone or a cordless phone. Ordinary PSTN phones are used as IP phones with analog telephony adapters (ATA). Following is an image of an IP phone:

Reasons to use SAN are as follows:
* Better disk utilization
* Fast and extensive disaster recovery
* Better availability for applications
* Faster backup of large amounts of data
Answer option D is incorrect. Installing SAN is expensive and it is not a reason to use SAN.

A hot site provides 100% uptime, but is quite expensive. In the case of a school, short downtime would not be detrimental to the business.
Answer option C is incorrect. Hot sites are only necessarily when 100% uptime must absolutely be achieved, and the excessive cost is justified.
Answer option A is incorrect. Each organization is different. Some will require a hot site, some won't Answer option B is incorrect. A school does not require a hot site. The cost is excessive and it is not needed for business continuity.