The writer wants to add information to the end of sentence 2 (reproduced below) to preview the line of reasoning in the passage. Unsurprisingly, neuroscientists warn that the constant use of smartphones alters the brain.
Which version of the underlined portion of sentence 2 most effectively accomplishes this goal?
A. brain, the complexities of which have long fascinated psychologists and psychoanalysts

B. brain, potentially undermining people’s ability to focus on serious school- and work-related tasks

C. brain, with potentially serious physiological and emotional costs

D. brain, which may have a profound impact on the still-maturing brains of young adults

E. brain, which many researchers claim may still be evolving