Final answer:
Random Assignment is the critical feature of an experiment that allows researchers to infer causation, as it controls for lurking variables and ensures differences between groups are due to the manipulated variable.
Step-by-step explanation:
The important feature of an experiment that allows researchers to infer causation is Random Assignment. This is crucial for developing a sound experimental design, as it ensures that the treatment and control groups are likely to be similar in all respects other than the variable being tested. By controlling for lurking variables and ensuring that the only difference between groups is the intervention being studied, researchers can attribute any observed differences in outcomes between the groups to the independent variable, which is the factor being manipulated in the experiment.