Identify true or false of the following statement

1.The simple linear regression is a useful tool for descriptive analysis but cannot be used for causal inference.

2.If all the relevant variables are included,then the OLS estimates will not be biased.

3.The fundamental challenge in using the potential outcomes framework to study causality is the inability to observe the counterfactual outcomes.

4.There are no omitted variables in a randomised controlled experiment.

5.As the multiple linear regression controls for additional variables,it is not subject to selection bias.