Jonathan is relatively new to his role as an IT technician at McHuge Company, Inc. While he's getting familiar with the details of McHuge's network and protocols, he's been leaning on his understanding of cloud stack theoretical layers to help him gain a more clear understanding of networking protocols at McHuge and troubleshoot issues when he encounters them. Which of the following about the cloud stack is correct?

a$.$ A customer of a private cloud has access to modify or manipulate cloud stack layers that are generally unavailable to customers of public clouds, such as the virtualization layer.

b$.$ Cloud stack is unlike the OSI model because it has five specific and standardized layers, whereas the OSI model's layers are dynamic.

c$.$ Cloud stack theory is applicable to SaaS and PaaS customers, whereas the OSI theory applies exclusively to public cloud network users.

d$.$ The physical layer $($layer $1)$ and the image layer $($layer $4)$ are the only layers of the cloud stack that can be manipulated in a public cloud.