I know I'm probably bugging you guys, but:
What system protects the body from foriegn substances?
It has 6 letters, and the 4th letter is a "u" and the 6th letter is a "t".
imune system
wait...its actually spelled immune system
No, but thanks! Unfortunately, it's only 6 letters long.
This is what I have of it so far:
_ _ _ u _ t