Q. If one doesn't want anyone else to read or write to a file named datfile, except through a program in a file filex , then he may use

• (A) chmod u+s filex ; chmod go_rw datfile
• (B) chmod 4711 filex ; chmod go_rw datfile
• (C) chmod 4711 datfile ; chmod go_rw filex
• (D) both (a) and (b)