Which of the following CRS upgrades are allowed?

Which of the following CRS upgrades are allowed? (Choose three).

A.
CRS 2.2 to CRS 3.5

B.
CRS 3.1 to CRS 4.0

C.
CRS 2.2 to CRS 4.0

D.
CRS 3.5 to CRS 4.0

Explanation: