The following ESX versions are supported for direct upgrading to vSphere 4 (Choose Two):
A.
ESX/ESXi 3.5
B.
ESX 2.1
C.
ESX 2.5.5
D.
ESX 3.0.0, 3.0.1, 3.0.2
Explanation:
vSphere Upgrade Guide ESX 4.0, ESXi 4.0, vCenter Server 4.0, vSphere Client 4.0, Page ‘Upgrade Support for ESX/ESXi:
ESX 3.0.0, ESX 3.0.1, ESX 3.0.2, ESX 3.0.3, ESX, ESXi 3.5 – Yes ESX 2.5.5 Limited Support’