Tornadoes(龙卷风) are one of the worst weather events on earth. Each year, tornadoes kill many people. The storms often carry homes, cars and trees from one place to another. And they can also destroy anything when they pass by.

      A tornado comes from a thunderstorm(雷雨) in the sky down to the ground. It is big at the top and small at the bottom.

      A tornado appears when winds in different directions meet in the cloud and begin to turn in circles. People can see tornadoes almost everywhere in the world. But most happen from late winter to middle summer. There is a second high season in November. During spring, warm air moves north and mixes with the cold air left from winter. In November, the opposite happens. Cold air moves south and mixes with the warm air left from summer.

      Tornadoes always come suddenly. Weather scientists have done something to predict(预测) tornadoes. But the storms often move too fast for people to protect themselves. Last year, tornadoes killed more than one hundred people in United States.

      Scientists say the best place to be in is a small room, without windows, in the middle the lowest part of a building when tornadoes come.

    3D printing is becoming more and more popular. We are now able to print things such as clothing, prosthetic limbs (假肢), musical instruments(乐器) and so on. People and businesses are able to create the things they need very quickly and easily using 3D printers.

    But can you imagine printing food? Some scientists are trying to revolutionize our eating experience by doing this. They hope that having a 3D printer in the kitchen will become as usual as the microwave or blender. Scientists say that they are easy to use: you simply have to choose a recipe and put the food "inks" into the printer. You can also change the instructions to make the food exactly how you want it. This means that it would be very quick and easy to create delicious meals.

    Using 3D printers to create your meals would also be saving the environment. There would be less need for traditional growing, transporting(运输) and packaging as food production would be quicker and easier.

    Printing food could also help people who suffer from dysphasia (吞咽障碍症). They could program (为…编程) the printer to print softer versions of their favorite foods so that they would not have trouble eating them.

    However, some people think that the future of 3D-printed food would be a disaster. It could take away many jobs, including those for growing, transporting and packaging food. Imagine a world where there was no need for farming or growing crops and the same tastes could be printed from a raw "food ink". Similarly, traditional cafes and restaurants might lose business. Also, there are worries about the printed food: is it really possible to get the nutrients (营养物) we need from food-based inks and gels?

    What's more, cooking and eating together with family and friends has long been a traditional and enjoyable activity. It is hard to imagine a world where the fun of cooking is dead and meals can be done at the touch of a button.                                                        

    Can plants eat people? Maybe not, but there are many plants that eat meat. Some of them are big and they can eat small animals. One famous meat-eating plant is the Venus flytrap(捕蝇草).

    The Venus flytrap is a very strange plant. It grows in dry parts of the United States. Its leaves are like the pages of a book. They can open and close very quickly. The fly (苍蝇) cannot get out. In about half an hour, the leaf presses (压) the fly until it is dead. Then, the plant covers(覆盖) the fly. Slowly, the plant eats the fly.

    Why do plants do it? Most plants get what they need from the sun, the air, and the ground (地面). In some places, the ground is very poor. It doesn't have all these important things, especially nitrogen(氮.). Animal meat has a lot of nitrogen, so many plants eat meat to get what they need.

    Let's hope that some of the bigger plants don't get the same idea!

    Like you, plants need good things like food, water, and minerals in order to grow. Usually they get these important nutrients(营养) from the rich soil(土壤) in which they're planted. But there's another way to grow plants that doesn't use soil. It's called hydrogenic gardening.

    "Hydrogenic" means "working with water." In a hydrogenic garden, plants grow with their roots in water, not in dirt. The water is filled with special food for the plants that gardeners have carefully measured and prepared.

    Hydrogenic plants grow quickly. In ordinary gardens, plants need time and energy to grow long roots that search the soil for food and water. In a hydrogenic garden, plants can use their energy to grow tall instead. And because there is no soil, there are no weeds and few insect pests(害虫). Gardeners don't need to spray(喷洒) plants with dangerous chemicals. Both the plants and the environment stay healthy. 

    Scientists hope that, one day, hydrogenic gardens may be able to help hungry people all over the world grow enough food-even in countries that have bad soil, or weather that is too hot, too cold, or too dry. And astronauts hope to take hydrogenic gardens with them to the spaceship they fly to Mars, so that they will always have fresh vegetables, and the fun of growing a garden without dirt.