a
Is the most impossible, because without this sentence pattern,
Holiday is a countable noun. Now holiday is singular, so add one.
What+a\an+ adjective+noun+subject+predicate+!
what
a
lovely
sky
it
Exactly!
If it is a plural noun, a\an
I won't add it.
what
lovely
human
they
Yes!
Of course, the subject+predicate can be omitted.
How ++ adjective \ adverb+subject+predicate+!
how
lovely
this
sky
Exactly!