Answer: Choice C) Multiplication property of inequality
The rule basically says that if you start with a < b and you multiply both sides by some positive number c, then a*c < b*c. The sign doesn't flip if you multiply both sides by a positive number. The sign will flip if c is negative. So we'll go from a < b to a*c > b*c if c is negative.
Example 1: 1 < 5 -2 > -10 ... multiplied both sides by -2; sign flips
Example 2: 3 < 7 9 < 21 ... multiplied both sides by 3; sign does not flip