Select the most appropriate option to substitute the underlined segment in the given sentence. If there is no need to substitute it, select No improvement.A phenomenon called the polar vortex has hit central and eastern parts of the United States. It has brought with it snow, brutally cold temperatures and potentially life-threatening wind chill.

• A. potentially life-threaten windy chills.
• B. No improvement
• C. potentially life-threatened wind chill.
• D. potential life-threatening wind chill.