The phrase (not sentence) 'long-standing army' is grammatically correct. It means 'an army that has been established for a long time.'
As the longstanding matriach of the family, it will be lonely since she will be away for the holidays.
there is a longstanding rivalry between USC and Clemson football teams.
As an adjective it is one word "longstanding" (traditional, done for many years).
an army :)
"How are you" is a correct sentence.
Yes, this sentence is correct.
You are palpitating. This is a correct sentence.
With the exception of not capitalizing the 'y' at the start of the sentence, it is a correct sentence.
(correct word is adjutant)He was promoted to adjutant last year, he deserved it as his services for the army were remarkable.
That sentence is grammatically correct.
no it is not a correct sentence.
no_____If the sentence is You do do that (meaning You are in the habit of doing that) the grammar is perfectly correct and the sentence 'does have correct grammar'.