It's my brother's first year studying English and the book they use at school has sentences like:
A is for Animal
B is for Beast
C is for Continent
D is for Den
and so on.
Shouldn't we use " " (or ' ') when we refer to a single letter inside a sentence? For example:
The letter "A" is the first letter in the alphabet.
The letter 'A' is the first letter in the alphabet.
Are there any cases when we should simply write an "A" alone?