The correct answer is chain of guard posts.
A. smokeless explosive
B. thin rope for rigging.
C. pen for horses
D. chain of guard posts
The correct answer is (D) Chain of guard posts; line (or circle) of sentries, guards, police, military posts, warships, etc. to enclose or guard an area, or to prevent access to a person, place, or thing.
Cordon comes from French corde.
Examples of use:
- The police created a cordon around the building as a safety measure.
- The soldiers immediately established a cordon around the airport.