In which of the following research methods does the process of hypothesis testing optimally safeguard the role of extraneous variables?

The experimental method best safeguards hypothesis testing against extraneous variables.

Its control conditions and randomisation isolate the independent variable's true effect.

The ex post facto method cannot control extraneous variables because events have already occurred.

The historical method studies past records and cannot manipulate or control conditions.

The descriptive survey method reports variables as they exist, offering weak control over confounds.

Random assignment spreads extraneous influences evenly across groups, which is unique to experiments.