The correct answer is C. 744.
The octal number 744 is used to make a file readable, writable and executable to the owner, readable and executable to group and others.
The first digit of the octal number represents the permissions for the owner of the file. The second digit represents the permissions for the group that owns the file. The third digit represents the permissions for everyone else.
In octal, 4 represents read permission, 2 represents write permission, and 1 represents execute permission. So, 744 means that the owner of the file can read, write, and execute the file, the group that owns the file can read and execute the file, and everyone else can read and execute the file.
Option A, 0, is not a valid octal number.
Option B, 755, is a valid octal number, but it does not make a file readable, writable and executable to the owner, readable and executable to group and others. It makes a file readable, writable, and executable to the owner, and readable and executable to group.
Option C, 744, is the correct answer.
Option D, 555, is a valid octal number, but it does not make a file readable, writable and executable to the owner, readable and executable to group and others. It makes a file readable and executable to everyone.