What is the difference between the "system conversion" and the "new implementation OF SAP S/4HANA transaction path. There are 2 option to this question.

What is the difference between the "system conversion" and the "new implementation OF SAP S/4HANA transaction path. There are 2 option to this question.
A . In the realize phase, data is converted and not migrated for system conversion
B . There are different upgrade cycles
C . In the realize phase, custom code is adjusted rather than developed for system conversion
D . SSCUI’s are used in system conversion for configuring SAP S/4HANA through the manage Your solution app

Answer: A,C