The last digit of the number obtained by multiplying the numbers \(81 \times 82 \times 83 \times ... \times 89\) is:
Answer: A
To find the last digit of a product, we only need to look at the last digits of the numbers being multiplied. The product includes the number 85, which has a unit digit of 5. It also includes several even numbers, like 82, 84, 86, and 88. The product of a number ending in 5 and any even number will result in a number ending in 0. Therefore, the unit digit of the entire product will be 0.