What is the purpose of a safety wire through a turnbuckle used to tension guy lines?

Answer: B. Prevent loosening of the turnbuckle from vibration

A safety wire through a turnbuckle prevents it from loosening due to vibration. Wind shakes guy lines all the time, and a loose turnbuckle could let a guy line go slack. The wire locks it in place.

Tip: Safety wire keeps the turnbuckle from turning.