Jellyfish are badly named. They are neither a fish nor made of jelly. Instead, their bodies are made up of 95%water and 5%solid matter. They have been in existence for at least half a billion years. Hence, they are older than dinosaurs. Surprisingly, they don’t have a brain, a heart, or lungs. You may wonder how they can possibly survive without these vital organs, but everything is for the heat. they don’t have lungs because their skin is so thin that they can absorb oxygen through it. They don’t need a heart to pump blood because they don’t have any. And they have a nerve net which is sensitive to touch below their outer skin. They respond to the changes in their environment using signals from the nerve net, so they don’t need a brain to process complex thoughts.

Their variety is nearly endless. Most of them are umbrella-shaped and have tentacles (触角). Some jellyfish have very long tentacles. However, they never sting(刺) themselves. That’s because the tentacles are very slippery and will only sting other animals. Most jellyfish have little or no vision, but they can detect light and ocean currents, which helps them to navigate and move. A few species can also recognize color and have a 360-degree view of their environment.

Jellyfish come in all sizes, from 0.5 millimoters to the giant Nomura’s jellyfish, which can measure up to two meters in diameter and weigh over 200 kilograms. While jellyfish are beautiful, they can also be dangerous. Some jellyfish toxins (毒素) can be deadly to humans, such as those from the box jellyfish and the Australian Irukandji, but deaths are relatively rare given the number of jellyfish-sting victims every year. In any case, it’s better to stay out of the way of any jellyfish you may see! You can go swimming with dolphins, but you definitely want to think twice before swimming with jellyfish.

Researchers from the University of Western Australia recently studied 3,000 middle and high school students. Among them were 618 teenagers with one parent who lived away from home for long periods of time because of work. The researchers wanted to know how the work of these "fly-in, fly-out" parents might influence the health of their children.

A higher percentage of teenagers who experienced the long work absence of a parent had emotional（情感的）or behavioral problems compared with those whose parents worked more traditional hours. This supports earlier research finding high percentages of emotional problems in teenagers who often returned to an empty house after school or whose parents were seldom at dinner.

Findings also suggest that parents don't have to be home all the time to be present in their children's lives, but it helps to be home at certain times. And the best parental presence for a teenager may sometimes be like a potted plant.

Many parents of teenagers have known this to be true and find ways to be present without trying to start a conversation. One friend of mine quietly does housework each evening in the sitting room where her teenagers watch TV.

They enjoy one another's company without the need to talk. Another friend usually accepts his daughter's invitation to work or read nearby while she sits and does her homework. Perhaps, that, at least for some families, is the best way for a teenager and their parents to stay close.

In fact, many years of research suggest that children use their parents as a safe base from which to explore the world. Studies tell us that young children quietly follow their parents' movements from room to room, even while carrying on with their own activities. Perhaps our teens, like babies, feel most at ease when their parents are still around. They don't want to stay away from parents who allow them freedom.

A new school year is at hand, so as parents we could offer our teenagers a "potted flower" as a gift, whose quiet and steady（稳定的）presence will give them a great day.

Humans have always been working Earth’s land, and they also have always been studying and hoping to work the land of Mars one day.

Planetary scientist Abhilash Ramachandran at the Lunar and Planetary Science Conference reported that Martian dirt may have all the necessary nutrients for growing rice, one of humankind’s most important foods. However, he emphasizes that the plant may need a bit of help to survive in perchlorate (高氯酸盐), a chemical that can be harmful to plants and has been detected on the surface of Mars.

Ramachandran says they want to send humans to Mars, but they cannot take everything there, especially food. He thinks it’s going to be expensive, but growing rice there would be ideal.

Ramachandran and his colleagues grew rice plants in a Martian soil simulant (模拟物). They also grew rice in pure potting mix as well as several mixtures of the potting mix and soil simulant. All pots were watered once or twice a day. The team found rice plants did grow in the artistic dirt of Mars. However, the plants developed slighter shoots and thinner roots than the plants that grew from the potting mix and hybrid soils. The researchers also tried growing rice in soil with added perchlorate. They sourced some rice varieties—modified to stand environmental stressors like drought—and grew them in Mars-like dirt with and without perchlorate. No rice plants grew in a concentration of 3 g of perchlorate per kilogram of soil. But when the concentration was just I g per kilogram, one of the rice varieties grew both a shoot and a root, while another managed to grow a root.

The findings are encouraging, suggesting that by changing to improve with one successful modified gene, humans might eventually be able to develop a rice cultivar suitable for Mars.