VMware vSphere ESXi, Microsoft Hyper$-$V and Citrix XenServer are instances of $$

Select one:

a$.$

Names of Hardware Systems that run Type $2$ Hypervisors.

b$.$

Names of common Type $2$ Hypervisors.

c$.$

Names of common Type $1$ Hypervisors.

d$.$

Names of Operating Systems that run Type $1$ Hypervisors.