懂你英语level6 unit1 part3 listening

Many scientists believe that the earth's magnetic field is due to the earth's rotation. Deep inside the earth is a solid iron core surrounded by a liquid metal outer core. The moving electric currents inside this liquid metal create a magnetic field. According to many scientists, what creates the earth's magnetic field?

It is now believed that the earth's magnetic field is about to reverse. This is called magnetic field reversal. Every 200000 to 300000 years, the earth's magnetic field reverses. In other words, the North and south magnetic poles switch places. This has happened many times in earth's history, but it has been happening more lately. What happens during a magnetic field reversal?

The earth's magnetic field is important because it protects us from the solar wind. The solar wind is a current of charged particles coming at us from the sun. When the solar wind near the earth, the earth's magnetic field deflects it away. This protects the earth from the radiation, which can be dangerous to life. How does the magnetic field protect the earth? What is the current of electrically charged particles? It absorbs the solar wind into the atmosphere. It comes at the earth from the sun. It deflects the solar wind away from the earth.

This time when the villagers heard his cries for help, they were convinced that it was another one of his pranks. Nobody believed that there was really a wolf, so they ignored his frantic calls for help, the wolf having nothing to fear, feasted on several of the sheep and then slipped back into the forest. What did the villagers do when they heard the boys calls for help?

  The past tense form can be used to express something that is unlikely or imaginary from the speaker's point of view, this condition expresses something that isn't a fact. If he had a car, he could drive us to school again. He doesn't have a car, so he can't drive us to school. It's a counter factual condition which means it goes against what we know or believe. Which condition is counterfactual or imaginary.

The past tense form can be used to express something that is unlikely or imaginary from the speaker's point of view, this condition expresses something that isn't a fact. If he had a car, he could drive us to school again. He doesn't have a car, so he can't drive us to school. It's a counter factual condition which means it goes against what we know or believe. Which condition is counterfactual or imaginary.

Many people think that the past tense form only indicates past time. However, that is only one of the possible meanings. The past tense form is also used to express something that is unlikely or imaginary from the speaker's point of view besides past time, what can the past tense form indicate?

Several years ago, jack had a young patient who showed him why his treatment didn't work. The patient's name was bob. He was 20 years old when he first came to see jack for help. The reason he came was that he had attempted suicide. Bob had attempted suicide.

Over the years, jack found that some patients improved with treatment, while others didn't improve at all. In some cases, a patient's response to treatment was the opposite of what was expected. What did jack know about the effectiveness of different treatments?

Several years ago, jack had a young patient who showed him why his treatment didn't work. The patient's name was bob. He was 20 years old when he first came to see jack for help. The reason he came was that he had attempted suicide. He wouldn't have come to see jack if he.