Examine the fragment below. A grammarian’s definition of gr...

Examine the fragment below.

A grammarian’s definition of grammar is:

I - The written rules governing when to use which forms or structures;

II - something you follow in order to use the language correctly;

III - That one particular variety of grammar is considered the “unusual” prescriptive.

(DeCapua, Andrea. Grammar for teachers. 2008. Springer)

Choose the correct option according to the context.