Fill in the blank with the most appropriate option
 

It was _________ hot that day and the cable suffered the brunt of the heat. 

Unbelievably 

The most appropriate word to fill in the blank is unbelievably.

The word unbelievably means to a great degree in a way that is very surprising or difficult to believe. It is generally used to describe the intensity. Here the sentence suggests that the day was very hot. Thus the word unbelievably is the most appropriate word to indicate the intensity of hotness.

The other words do not fit the blank as well.

• Treacherously means involving betrayal or deception.
• Acceptably means in an adequate or satisfactory way.
• Unfailingly means in a reliable or unchanging way, always.