Answer: Toe rail, option C.
Explanation: The guardrail is a security system, used to control the possible movement of people.
The mid-rail and top-rail are rails at the height of the knees and the hips, more or less.
The Toeboard is a little "bracket" at the height of the feet, which may prevent someone to slide under the mid-rail.
The third option, "Toe Rail" is not a feature of a guardrail.
