Which of the following parts of this path is considered to be a security risk?

The root user types cho $PATH and sees the following output:
.:/bin:/usr/bin:/sbin:/usr/X11R6/bin:/usr/src

Which of the following parts of this path is considered to be a security risk?

A.
.

B.
/usr/src

C.
/sbin

D.
/usr/X11R6/bin