What is a valid, minimum set of steps to properly upgrade this environment to NSX?

An administrator wishes to upgrade to NSX from the following infrastructure:
vCenter Server 4.1
vShield 5.0
ESXi hosts 4.1
What is a valid, minimum set of steps to properly upgrade this environment to NSX?

A.
1. Upgrade vCenter Server 4.1 to vCenter Server 5.5
2. Upgrade vShield 5.0 to vShield 5.5
3. Upgrade ESXi hosts to ESXi 5.1 or greater
4. Install the NSX upgrade bundle

B.
1. Upgrade vCenter Server 4.1 to vCenter Server 5.1
2. Upgrade vCenter Server 5.1 to vCenter Server 5.5
3. Upgrade ESXi hosts to ESXi 5.1 or greater
4. Install the NSX upgrade bundle

C.
1. Upgrade vCenter Server 4.1 to vCenter Server 5.5
2. Upgrade ESXi hosts to ESXi 5.1 or greater
3. Install the NSX upgrade bundle

D.
1. Upgrade vCenter Server 4.1 to vCenter Server 5.5
2. Upgrade vShield 5.0 to vShield 5.5
3. Install the NSX upgrade bundle