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I ……..practised playing the piano last week, but I was lazy and now I regret not practicing it.

a) should have b) could have

I think both A & B are OK. Am I right? I think there may be a difference between 'should have + pp" and 'could have + pp" , but I don't know it.

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should have — it would have been advisable (for me to practice)
could have — it would have been possible (for me to practice)

Both are OK, but if you had to pick one, a) would be better.

CJ