Question

what is the best preventive measure to prevent falls from occurring due to an opening in a wall or floor?
the opening must be marked with fluorescent paint.
the opening must be repaired before work can continue.
large signs are the only measure that must be implemented.
the opening must be guarded or covered.

Explanation:

Marking with fluorescent paint or using large - signs only alerts but doesn't physically prevent falls. Repairing before work continues might not be immediately possible. Guarding or covering the opening physically blocks the risk of falling through it, which is the most effective preventive measure.

Answer:

The opening must be guarded or covered.