"Dog" is underlined? So you're supposed to replace that word with a synonym that gives "a positive tone"?
Please re-think.
Yes, your revised sentence is correct in terms of rewriting it using a positive tone. You've successfully transformed the original sentence by adding the adjective "big" to describe the dog, which conveys a more positive impression. Additionally, you maintained the main idea of the original sentence while enhancing it with a positive connotation.
