4 . Imagine the sound of a dog walking across a tile floor, the “click, click, click” of its claws tapping against the ground. Now, imagine a cat walking across the same floor — the difference is the cat moves in total silence. Cats can fully retract (缩回) their claws, giving them superior ability to remain silence.

But why do cats have retractable claws, whereas dogs do not?

It all comes down to how cats and dogs use their claws. Cats use their claws primarily to attack their target, said Anthony Russell, an evolutionary biologist at the University of Calgary in Alberta, Canada. They use their front claws to grab and hold on to their target and their back claws to cut open the target’s belly.

Cats need to keep their claws sharp to secure that next meal. Extended all the time, their claws would get less sharp as they scrape the ground, much like how a nail file deals with sharp points on a human fingernail.

Dogs, on the other hand, are social hunters. They work in groups to take down larger animals, wearing their target out over longer distances. For dogs, “if you’re hunting a moose or something, you wander along for kilometres and bite it until it is fatigued, and then you all jump on it,” Russell said. “Whereas cats essentially have a short burst, and then it’s over. Either the target gets away, or the target is captured.”

With more hunters working together, it’s less important for dogs to be able to grab and hold onto their target, so they don’t have to keep their claws as sharp. Sheer numbers are enough to give them the advantage.

But dogs’ claws aren’t completely useless. Dogs’ claws help them stand firmly on the earth and change directions quickly — a useful adaptation for pursuing target over long distances.

In nature’s silent dance, cats’ retractable claws are knives for quick attacks, while dogs’ strong claws make them good chasers. Each claw tells a tale of adaptation made to their unique hunting styles.

6 . The sun is setting. I’m sitting on a rock top on the Jurassic Coast with my family. We are _________ and dusty after a long day of hiking. We are on a 630-mile route plan. Our only _________ is to complete it as a family by the time the children have finished secondary school.

Out in the wild, I have _________ something magical happening. My children are _________ all the time. They are capable of _________ 10 miles a day carrying their own pack. On the trail, they don’t _________ eating simple noodles or the rain that pours down. It _________ me how they do it, waking each morning totally _________, like someone hits the reset button.

After resting, with packs returned to our _________, we set off with no real plan other than walking onwards. I love the freedom that we just walk __________ until something catches our fancy.

As I walk ahead, I reflect on why we want to be out here. Mostly, I think it’s because it slows us down and __________ us deeply in nature. It’s also turned out to be about the people we meet along the way, like the kind couple who __________ to give us a lift back, or the group of teens who __________ us to join in their game. The trail gifted us meaningful __________ with these kind strangers. So far we’ve walked 120 miles. Maybe it’ll take us several years to complete the whole thing, but I’m sure there will be much __________ waiting for us ahead.

8 . A 72-year-old Chinese retired physics professor becomes an Internet celebrity. In her short videos, Wu Yuren often uses everyday objects like eggs and coins as props for her experiments. In one video for example, when explaining cosmic rays in space. she grabbed a broom, ran her hand down the broomstick to the thin brush attached, to illustrate how the energy of the rays gradually weakens and disperses. She also explained rocket launches by blowing up a balloon. These interesting science videos have attracted over 1 million followers, many calling her “science grandma”

It’s said that Grandma Wu writes all her video scripts by herself, and she often works with young team members till late at night, just to plan each shoot down to the last detail. For some physics principles that are hard to present, she would discuss them with other professors to work out something easy for people to understand.

Many youngsters are greatly touched by Grandma Wu’s sense of responsibility and mission to communicate physics ideas to the public, especially teenagers. Meanwhile, her lifestyle, embracing new technologies to maximize her value, inspires people in particular.

In recent years, Chinese short-video sharing platforms saw a rise of such elderly Internet celebrities like science grandma. For example, there’s “Grandpa Amu”, an experienced carpenter who turns ordinary wood into exquisite items without a single nail or a drop of glue. "Shaanxi Old Qiao", or Grandpa Qiao, teaches people to cook Shaanxi’s local cuisines in his videos. These noodles and all are so tempting that even kitchen rookies couldn’t help trying.

With the technology boom and the help of young people, many Chinese seniors are opening up a new digital world, and are communicating with the world better through the web. Plus, all this also shows society’s respect and affection for the elderly.