The answer is C. Sultry.
The other four words (A, B, D, and E) all describe temperature. Sultry, on the other hand, describes a type of weather that is hot and humid.
Cool is a word that describes a temperature that is below average. Warm is a word that describes a temperature that is above average. Hot is a word that describes a temperature that is very high. Humid is a word that describes a high level of moisture in the air.
Sultry weather is often described as being oppressive and uncomfortable. It can be caused by a combination of high temperatures and high humidity. Sultry weather can make it difficult to breathe and can lead to dehydration.