I agree with Sound Shift. I could, probably, say this one in exactly the way I punctuated it - "3 years ago" would come as an afterthought if I was unable to remember which year exactly it was that I started smoking. Otherwise, the clean version would be:I have been smoking since ..... 3 years ago?
The first one is fine.Thanks! It seems that all your attention is focused on the adverbial clause. What if I make the sentences into:
I have been smoking since last October?
I have picked up smoking since last October?
Do they mean the same now?
Yes, that's right. You can smoke continuously from a certain date in the past until today, so you would use the present perfect continuous:"Pick up" is a one-time action, meaning start. You can't have been doing it continuously either for the past three years or since last October.