The term "Just between you and I" is not a sentence. It is a prepositional phrase.
The pronoun "I" is incorrect. The pronoun "I" is a subject pronoun uses as part of the compound object of the preposition.
The pronoun "you" is correct. The pronoun "you" can function as a subject or an object in a sentence.
The correct prepositional phrase is: Just between youand me...
Between David and him would be the correct grammar in this case.
"On a train" is correct grammar.
Grammar.
The grammar is correct as it is.
No. The correct grammar is; "Yes, I have a girlfriend."
The correct grammar is "Between you and me."
"July has just been started" is not correct grammar, instead the correct grammar is "July has just started."
Between David and him would be the correct grammar in this case.
The correct grammar/spelling is in between.
The correct grammar is YOU AND I if used as a subject, e.g. ""You & I will have a jolly good time". Correct grammar requires YOU AND ME if used as an object, e.g. "This is just between you and me" "I" designates a subject and "me" designates an object.
No, "will be had" is not a correct grammar. The correct grammar would be "will have."
It depends on context. For example, in a conversation between two people: Person #1: Those items are not for sale. Person #2: Which are? In that context, it is understood that "Which are?" means "Which items are for sale?"
Both are correct. Most people use the latter.
Yes. "The car that just passed was theirs" is grammatically correct.
No, it is correct grammar, not a correct grammar.
The correct grammar is: "Are those correct?"
"On a train" is correct grammar.