Final answer:
The property that justifies Jozelle's step is the Associative Property of Addition.
Step-by-step explanation:
The property that justifies Jozelle's step of rewriting the expression (ab + a + b + 1) as (ab + a) + (b + 1) is the Associative Property of Addition (option b). This property states that it doesn't matter how we group numbers when adding them, the result will be the same. In this case, Jozelle grouped ab and a together and b and 1 together using parentheses. This step is valid because addition is associative, meaning the order in which numbers are grouped does not affect the result.