I've been spending a lot of time doing that.
...
I've been concentrating on one thing.
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I've been taking it easy.
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I haven't had time to do something.
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I've been getting nowhere.
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I've been having problems with that.
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I've saved a lot of time
...
I've wasted a lot of time.
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I've been doing my best.
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I've been making good progress.
...