The right answers are "By identifying areas of the United States that are considered vulnerable to attack " and "By excluding people that may pose a threat to national security from military areas ".
It is the responsibility of the president to identify vulnerable areas of the country and strengthen security at these places to prevent attacks of violence, crimes, or any other that is dangerous to the security of the nation. It is also his responsibility to exclude and monitor persons who may pose a threat to the national security of military areas. These people are dangerous because they can facilitate internal attacks in the country and in addition, they can know the vulnerable areas.