To study the effects of noise on worker productivity, researchers have on group of subjects work in a noisy room and a second group work in a quiet room. to ensure that any differences in the productivity of the two groups actually results from the different noise levels to which the groups are exposed, the researchers would use: 1) the case study 2) correlational measurement 3) naturalistic observation 4) replication 5) random assignment

5) random assignment          

Explanation:

Random assignment: It is used in a psychological experiment, as a chance procedure to make sure that every single participant has the same probability of getting assigned in any mentioned group. The study participants are being randomly assigned to each group, the same as in the experimental group.

Example: In an experiment, every participant gets assigned in either an experimental group or a control group.

the answer to your question is,

old stone age.

-mabel < 3

answer; one person; monarch;