Here we need to modify the size of the VM to increase the number of vCPU's assigned to the VM. This can be included as a task in the runbook. The VM size property can be modified by a runbook that is triggered by metrics, but you can schedule it monthly.

C: Scheduled vertical scaling could be a solution, but then you don't need a scheduled runbook and it states that it does not support multiple active instances. Scale Set is not a n option.

E: DSC is only useful to keep the resources on a VM (OS, File shares, etc.) in a consistent state, not to change VM properties.