Your ISP $($Internet Service Providers$)$ gives you an IP address, and it's public knowledge which ISPs have access to which IP addresses, thus:

a$.$ geotargeting is illegal due to privacy concerns.

b$.$ GPS is based on IP addresses

c$.$ geotargeting cannot be used to serve advertising.

d$.$ IP addresses can be used in geotargeting $.$

e$.$ IP addresses are primarily used for identifying device manufacturers.