The correct answer is: A. crash conversion.
A crash conversion is a systems conversion technique of totally removing the existing system and immediately implementing the new system. It is a high-risk approach that is only used when there is no other option.
A phased conversion is a systems conversion technique in which the new system is implemented in stages, with the old system being gradually phased out. This is a less risky approach than a crash conversion, but it can take longer to complete.
A pilot conversion is a systems conversion technique in which the new system is first implemented in a small part of the organization, and then rolled out to the rest of the organization if it is successful. This is a less risky approach than a crash conversion or a phased conversion, but it can take longer to complete.
A parallel run is a systems conversion technique in which the new system is run alongside the old system for a period of time, and then the old system is phased out. This is a low-risk approach, but it can be expensive to run two systems at the same time.
None of the above is a systems conversion technique of totally removing the existing system and immediately implementing the new system.