Which THREE of the following are true?

When a new computer system is being implemented there are several possible methods for managing the changeover from the old system to the new system.

Which THREE of the following are true?
A . Phased changeover is the safest and slowest method of changeover.
B . Phased changeover moves individual portions of the business to the new system one at a time.
C . Pilot changeover moves the simplest part of the business to the new system first.
D . Parallel running involves keeping the old system running, normally until certain data retention criteria are met or confidence is gained, while the new system deals with the new workload. Data input is usually carried out on both systems.
E . Direct changeover, or Big Bang is only used when the systems are significantly different such that comparing the outputs of the two systems is largely irrelevant.
F . All methods of changeover carry high risk and it is the preparation, consideration of data compatibility and data cleansing before the changeover which has the biggest impact on the smoothness of the transition.

Answer: B,D,F