Which of the Following Statements About the Reliability Requirement Level

Which of the following statements about the reliability requirement level are true? (Choose three.)

A) Faults seldom occur in the system software or hardware.
B) System functions are affected by faults.
C) System functions are affected by faults but can rapidly recover.
D) System functions can be ensured by using redundancy design, switchover policy, and high success rate in switchover.