Answer:
C
Step-by-step explanation:
0.031 * 0.31 = 0.00961
Why A is incorrect: If you count how many digits there are on the right of the decimal, there are 5 digits. Therefore, the product has more than four decimal places.
Why B is incorrect: 0.31 can be written as 0.31000. If you compare 0.00961 to 0.31000, it is obvious that 0.00961 is less than 0.31000. BUT, 0.031 can be written as 0.03100, and if you compare 0.03100 to 0.00961, it is obvious that 0.00961 is STILL less than 0.03100. The product is less than 0.31 and less than 0.031, therefore this answer is incorrect.
Why C is correct: ^^^
Why D is incorrect: It has been argued that 0.00961 is already less than 0.31000 and 0.031000, and as you may already know, these digits are less than 1. We can conclude that 0.00961, our product, is less than 1. 1 can also be written as 1.00000, and if we compare it to 0.00961, 1 is greater. 1 is a whole number and 0.00961 is not.