*NEED ASAP*

An online retailer wants to study whether more
lenient return policies increase purchasing
behaviors. They select a random sample of
2000 customers who have made purchases in
the past year.
The
company
ranks the customers according to
total cost of purchases made the previous year.
For every 2 customers, in order, from the list,
the online retailer randomly assigns one
customer to the treatment group and the other
to the control group.
What type of experiment design is this?

Systematic
Cluster
Randomized block
Matched pairs
Completely ramdomized