Question #N798

The sentence "The cat sat on the mat, watching the birds." is grammatically correct, but it lacks a clear subject. Which of the following is the BEST way to rewrite the sentence to include a clear subject?
A. As the cat sat on the mat, watching the birds.
B. The cat, sitting on the mat, watched the birds.
C. While watching the birds, the cat sat on the mat.
D. The cat, it sat on the mat, watching the birds.