阅读理解
Smartphones have by now been implicated in so many crummy outcomes—car fatalities, sleep disturbances, empathy loss, relationship problems, failure to notice a clown on a unicycle—that it almost seems easier to list the things they don't mess up than the things they do. Our society may be reaching peak criticism of digital devices. Even so, emerging research suggests that a key problem remains underappreciated. It involves kids' development, but it's probably not what you think. More than screen-obsessed young children, we should be concerned about tuned-out parents. Yes, parents now have more face time with their children than did almost any parents in history. Despite a dramatic increase in the percentage of women in the workforce, mothers today astoundingly spend more time caring for their children than mothers did in the 1960s. But the engagement between parent and child is increasingly low-quality, even ersatz. Parents are constantly present in their children's lives physically, but they are less emotionally attuned. To be clear, I'm not unsympathetic to parents in this predicament. My own adult children like to joke that they wouldn't have survived infancy if I'd had a smartphone in my clutches 25 years ago. To argue that parents' use of screens is an underappreciated problem isn't to discount the direct risks screens pose to children: Substantial evidence suggests that many types of screen time (especially those involving fast-paced or violent imagery) are damaging to young brains. Today's preschoolers spend more than four hours a day facing a screen. And, since 1970, the average age of onset of "regular" screen use has gone from 4 years to just four months. Some of the newer interactive games kids play on phones or tablets may be more benign than watching TV or YouTube, in that they better mimic children's natural play behaviors. And, of course, many well-functioning adults survived a mind-numbing childhood spent watching a lot of cognitive garbage. (My mother—unusually for her time—prohibited Speed Racer and Gilligan's Island on the grounds of insipidness. That I somehow managed to watch every single episode of each show scores of times has never been explained.) Still, no one really disputes the tremendous opportunity costs to young children who are plugged in to a screen: Time spent on devices is time not spent actively exploring the world and relating to other human beings.
单选题21.We can learn from the first two paragraphs that smartphones______.