The correct answer to the question is C) is necessary to maintain a safe environment for students.
The underlined portion "to keep things safe for the community might be a necessary thing" refers to the students as 'the community' and appeals to its safetiness by enhancing the school locker searches as a necessary action however it leaves the statement open for discussion or doubt hence, by changing it to "A school's right to search student lockers is necessary to maintain a safe environment for students" leaves no doubt about what needs to be done and provides a benefit after the action is done.