Katz doesn't necessarily agree with Brynjolfsson and McAfee that new technologies will lead to sluggish job growth, saying in the fifth paragraph that "no historical pattern shows these shifts leading to a net decrease in jobs over an extended period." However, he's not sure that will remain true, explaining in the sixth paragraph that no one can be certain what is going to happen to the workplace as a result of these new technologies: "If technology disrupts enough, who knows what will happen?"
Choices A, B, and D are incorrect because it would not be accurate to characterize Katz as being alarmed (choice A), unconcerned (choice B), or optimistic (choice D) about today's digital technologies. Rather, it's clear from the conclusion of the sixth paragraph that Katz isn't sure how technological advancement will affect the workplace: "If technology disrupts enough, who knows what will happen?"