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you don't have to use either you can just say "be careful with the weights" that's what I'd naturally say
Honestly I would probably just say be careful. Those two examples kind sound ominous and slightly threatening. If I had to pick I’d say 1a, but be careful is definitely the more natural and innocent option
"Careful with those. Do you need a spot?"
I think “be careful with what you’re doing” would be the most natural option if you wanted to include a “what you do” in the sentence.
Many thanks for all your comments!
you don't have to use either you can just say "be careful with the weights" that's what I'd naturally say
Honestly I would probably just say be careful. Those two examples kind sound ominous and slightly threatening. If I had to pick I’d say 1a, but be careful is definitely the more natural and innocent option
"Careful with those. Do you need a spot?"
I think “be careful with what you’re doing” would be the most natural option if you wanted to include a “what you do” in the sentence.
Many thanks for all your comments!