I understand you all along.
No. The correct way is: I've understood you all along.
No - the sentence 'Had never been experience' is not a correct sentence.
No, that sentence is not correct. That sentence should be: If you have been in love for 6 years.
"He could not have been there" is the correct sentence. It conveys the idea that he was unable to have been at the specified place.
Being able is the correct version of the sentence. You can use it as a fragment of any sentence.
The correct sentence is: "Have you ever traveled before?"
A central fund for EGMM has been opened.
Yes, "How long have you been living in Oxford?" is a good sentence.
The use of the word in the sentence you quote is in the sense of having been perceived as being rude to an elder. So yes, the sentence is correct.
Your account has not been generating much traffic.This sentence is grammatically correct. It is negative present perfect continuous.
Yes, the grammar in the sentence "The attached invoices have been confirmed" is correct.
The correct punctuation for "No, I have never been to Europe" is to add a comma after "No."