why backups of ESX 3.x VMs created with VMware Data Recovery take longer than backups of ESX 4.x VMs?

Which of the following explains why backups of ESX 3.x VMs created with VMware Data Recovery take longer than backups of ESX 4.x VMs?

A.
VMware Data Recovery uses data deduplication technology with ESX 4.x VMs, but not with ESX 3.x VMs

B.
VMware Data Recovery uses changed block tracking functionality with ESX 4.x VMs, but not with ESX 3.
x VMs

C.
VMware Data Recovery uses the VMware vStorage APIs with ESX 4.x VMs, but not with ESX 3.x VMs

D.
VMware Data Recovery uses Microsoft’s Volume Shadow Copy Service (VSS)with ESX 4.x VMs, but not with ESX 3.x VMs

Explanation:
VMware Data Recovery Administration Guide Data Recovery 1.1, page 8.

For virtual machines created in vSphere 4.0, the Data Recovery appliance creates a
quiesced snapshot of the
virtual machine during the backup. The backups use the changed block tracking
functionality on the ESX hosts.

For each virtual disk being backed up, it checks for a prior backup of the virtual disk. It
uses the change-tracking functionality on ESX hosts to obtain the changes since the last
backup. The deduplicated store creates a virtual full backup based on the last backup
image and applies the changes to it.

NOTE These optimizations do not apply to virtual machines created with VMware
products prior to vSphere

4.0. For example, change tokens are not used with virtual machines created with Virtual
Infrastructure 3.5 or
earlier. As a result, virtual machines created with earlier VMware versions take longer to
back up