Sentence correction: Structure question

Even though they do not sting or bite, many people are surprised to learn that cicadas are benign creatures because they appear threatening.

A. many people are surprised to learn that cicadas are benign creatures because they appear threatening
B. many people are surprised to learn that cicadas are benign creatures ,who appear threatening
C. surprising to many people is to learn that cicadas are benign creatures because they appear threatening
D. cicadas appear threatening, therefore, many people are surprised to learn that they are benign
E. cicadas appear threatening, which causes many people to be surprised when learning that they are benign

Pls give the answer as well as the the explanation for the above question.