Final answer:
The best estimate for the product of −453 and −6756, after rounding to one significant figure, is 3,500,000, which suggests that 3,000,000 (Option A) is the closest estimate.
Step-by-step explanation:
To find which expression will best estimate the product of −453×−6756, we can round these numbers to one significant figure and multiply them together. Therefore, −453 rounds to −500 and −6756 rounds to −7000. The product of these estimates is 500×7000, which equals 3,500,000. The closest answer choice to our estimate is 3,000,000 (Option A).