present perfect - "I have been 'verb-ing'" vs. "I had been 'verb-ing'"

A. I have been studying English for one year.

B. I had been studying English for one year.

Could one who hears those sentences argue that "A" case implies "and I am still studying it" whereas "B" case implies "and I am no longer studying it"? If so, how are different in time frame the following sentences?

1. 
   
   

   I worked in Colombia for ten years when the manager sent me to Italy.

   
   


2. 
   

   I have been working in Colombia for ten years when the manager sent me to Italy.

   
   


3. 
   

   I had been working in Colombia for ten years when the manager sent me to Italy.

   
   

Please, consider that the real situation is that I worked in Colombia from 1963 to 1973 and, for some reason, 1, 2 or 3 must be written today.

However I'm under the impression that only the "3" case is grammatical or, in any case, correct in reference to the real situation, although "1" case seems to be salvageable deleting the preposition "for".

Can anybody explain?

Answer

Sentence A states that you have been studying right up to the very moment of speaking. It says nothing in particular about your future plans; it will usually be taken to imply that you will continue to study, because a present state is presumed to continue, but this can be overridden:

I have been studying English for one year, and I'm sick of it. I quit.

Sentence B states exactly the same thing about some moment (the Reference time) in the past: you had been studying up to that moment. In this case there is no implication either way, for the focus is on the Reference time, not what happened subsequently. Both of these work:

I had been studying English for one year before I switched to French.

I had been studying English for one year when I was offered the Chair in English Language and Literature at the University of Brescia.

Sentence 1, if taken literally, means you were working in the wrong place! Sentence two is ungrammatical: I have been implies you are speaking of the present, but sent speaks of the past. Only Sentence 3 fits the circumstances you describe: you worked in Colombia up to the point where you were sent to Italy.