Easy for noobs choose one that will sound right:
(with this objective) or (too) or (however) or (thus) or (frequently)

However.

Explanation:

The first sentence provides good effects. But, the sentences after it provides some of the negative effects of electronics. Because of the change of thought, you would use a word that shows the difference between the sentences. "However," is a good transition that changes the what the reader views.

answer:   the correct answer is: [a]:  

                          →     " theme " .

hope this !

    best wishes to you in your academic endeavors

            — and within the community!

what passage are you referring to