My personal choice from those presented is B-2
In group A the word 'now' would not be commonly used. Rather than saying 'one', 'a'is more common.
In group B the phrase 'at this' is out of place and should be dropped.
Hope it helps :D
Edit:*
Glad it helped :D
I would choose "6) It has been a year now since you promised me."
If I were to rephrase it to my own vernacular I would say:
"It has been a year since you promised me that ..."
"...you would stop shaving the cat."
"...you would get me a pet monkey."
"...was the last time you were going to dye your hair purple."
Note the different use of the word 'that' in the third example. In the first two, 'that' refers to the promise. In the third, 'that' refers to the time they performed the act they then promised not to do again.
'Now' can be used in two ways conversationally. First is to denote the present time: "Now is the time for change."
The other way is as a demand for attention: "Now, a year ago you promised me that you would get a haircut". In this case (I think) there is an unstated "Pay Attention", so the second sentence could be restated PAY ATTENTION NOW, A year ago you promised..."
I'm not a grammarian though, so I am Glad it helped :D
I would choose "6) It has been a year now since you promised me." If I were to rephrase it to my own vernacular I would say "It has been a year since you promised me that ..."
"...you would stop shaving the cat."
"...you would get me a pet monkey."
"...was the last time you were going to dye your hair purple."
Note the different use of the word 'that' in the third example. In the first two, 'that' refers to the promise. In the third, 'that' refers to the time they performed the act they then promised not to do again.
'Now' can be used in two ways conversationally. First is to denote the present time: "Now is the time for change."
The other way is as a demand for attention: "Now, a year ago you promised me that you would get a haircut". In this case (I think) there is an unstated "Pay Attention", so the second sentence could be restated PAY ATTENTION NOW, A year ago you promised..."