488. Misuse of friendly as an adverb
(X) Andrew behaves friendly.
(O) Andrew behaves in a friendly way.
The adverbial form is in a friendly way.
"Friendly" is an adjective: a friendly game, to have friendly relations with one's neighbors, etc.
489. Misuse of truth as an adjective
(X) Is it truth that Diana's very ill?
(O) Is it true that Diana's very ill?
"Truth" isn't an adjective but a noun.
The adjective is "true", and we use it with no article between "it and the verb to be."
490. Misuse of plenty as an adjective
(X) Mike had plenty work to do.
(O) Mike had plenty of work to do.
"Plenty" isn't an adjective, but a noun(or a pronoun) meaning a large number or amount.
The adjective is "plentiful." Oranges are cheap now because they are plentiful.