$16-$ Why is there a problem with the addressing scheme above?

a$.$ There is an overlap between $192\mathrm{.}168\mathrm{.}1\mathrm{.}220/30$ and $192\mathrm{.}168\mathrm{.}1\mathrm{.}192/27$

b$.$ There is an overlap between $192\mathrm{.}168\mathrm{.}1\mathrm{.}188/30$ and $192\mathrm{.}168\mathrm{.}1\mathrm{.}192/27$

c$.$ There is an overlap between $192\mathrm{.}168\mathrm{.}1\mathrm{.}128/27$ and $192\mathrm{.}168\mathrm{.}1\mathrm{.}188/30192\mathrm{.}168\mathrm{.}1\mathrm{.}188$ is not a valid network address.

d$.192\mathrm{.}168\mathrm{.}1\mathrm{.}220$ is not a valid network address.