Final answer:
The constant in the algebraic expression 3ab + 2a - 5b + 7 is D. 7, as it is the only term without any variables.
Step-by-step explanation:
The constant in the expression 3ab + 2a - 5b + 7 is D. 7. A constant in an algebraic expression is a term that does not contain any variables and thus does not change its value. In the given expression, the term 7 is the only one without a variable, making it the constant term. All the other options, 3ab, 2a, and -5b, contain variables and are therefore not constants.With cluster sampling, the population is divided into clusters, such as geographical areas, and then whole clusters are randomly chosen, with all members of those clusters being included in the sample. Non-probability sampling methods like convenience sampling involve choosing participants that are easily accessible, which may lead to biased results since the sample may not be representative of the entire population.