Researchers may control factors that might influence a dependent variable by means of

a) random assignment.
b) replication.
c) naturalistic observation.
d) operational definitions.

A) random assignment.

Explanation:

Random assignment is a technique used in experiments and it refers to putting a subjects of experiment into different experimental groups by chance (random). This is the best way to ensure that differences between formed groups are due to experimental treatment and to avoid experimenter bias.

answer; i believe the correct answer is (replication is not conservative);

a community that experiences major changes undergoes progress