Anybody who’s noticed so many sweaty Sunday-morning photos on the Internet must think that marathons have recently regained popularity．According to Running USA，an organization that tracks the sport’s growth，52 percent of runners today track themselves with some sort of GPS-enabled device，like a smart phone or a fitness tracker．This statistic has likely played a role in running’s growing appeal--the easily available tracking information has attracted people to the sport，and kept them going，for it’s possible for anyone to see in real time how it’s affecting their bodias.
Today，free smart phone apps can give runners information on things like the number and length of their steps，their heart rate，even the estimated volume of oxygen they consume per minute．All this information can act as a reward and a motivator for the runner．“It’s one thing to hear encouragement from a coach．”Bryan Boyle，editor of Runner’s World magazine，explains．“It’s quite another，however，to appreciate-at a glance-progress made during weeks and months of running．’’
But run—tracking technology doesn’t just help runners train harder. It also gives them the power to train more intelligently．Recreational runners today no longer have to guess how far or how fast they’ve run，or what their body is doing．If they can monitor their heart rate，they can make sure they’re hitting the most strategic pace on each run，which can significantly increase their chances of having a positive experience on the course during race day．
No matter how much technology can promote the experience of running，though，many runners argue that the biggest benefit of the sport remains the chance to get outdoors，away from the computer，for an hour．“There’s so much more to experience，” adds Boyle．“fresh air，travel，shoot，just overall feeling better．There’s no app for that．”
We can infer from the first paragraph that     ．

A．people enjoy posting sports pictures on the Internet

B．Running USA plays a key role in the growth of running

C．tracking technology is drawing more people on the road

D．run—tracking devices help people run faster than before

Which of the following questions are the second and third paragraphs intended to answer?

A．What information can run—tracking devices provide for the runners?

B．How is the run—tracking technology popularizing running?

C．In what way is run—tracking technology developed?

D．Why do people have to rely on wearable devices in modern society?

As for the experienced runners，what attracts them most is    ．

A．the exciting experience technology brings them

B．a chance to enjoy nature outdoors

C．becoming popular on social media

D．being cool with a new wearable device on the road