Even though they do not sting or bite, [u]many people are surprised to

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

Before answering this question, I would like to know the source of this question because the options are poorly constructed. Every option contains a mistake or other. Option D is best among the rest, but has flaws as well.
Even though they do not sting or bite, cicadas appear threatening, therefore, many people are surprised to learn that they are benign

The only problem with this sentence is that THEREFORE acts as CONJUNCTIVE ADVERB, which MUST be preceded by semicolon & followed by a comma as it is in the middle of the sentence. Correct sentence should be
Even though they do not sting or bite, cicadas appear threatening; therefore, many people are surprised to learn that they are benign.

I would suggest everyone to stop referring using this source for SC.

The source is Princeton Review 1,012 practice questions.

OPEN DISCUSSION OF THIS QUESTION IS HERE: even-though-they-do-not-sting-or-bite-many-people-are-surprised-to-le-199626.html