Which of the following is the best method for radiation protection of the operator?

Operators of radiographic equipment should use barrier protection when possible, and barriers should contain a leaded glass window to enable the operator to view the patient during exposure. When shielding is not possible, the operator should stand at least two meters from the tube head and out of the path of the primary beam (ADA 2006).   White and Pharoah's Oral  Radiology Principles and Interpretation 8th edition