Which statement about subnetting is correct?

Question $40$ Answer

a$.$

Subnetting applies only to IPv$4$ networks, unless you are using Classless Inter$-$Domain Routing $($CIDR$).$

b$.$

Both IPv$4$ and IPv$6$ provide for subnetting, but the much larger IPv$6$ address field makes this a lot simpler to design and manage.

c$.$

Subnetting in IPv$4$ involves the CIDR protocol, which runs at Layer $3$; in IPv$6,$ this protocol, and hence subnetting, is not used.

d$.$

Because the subnet mask field is so much larger in IPv$6,$ it is easier to subnet in this newer protocol stack than in IPv$4.$