1. Lightning is a spectacular and somewhat frightening discharge phenomenon, accompanied by lightning and thunder. Lightning is usually produced in cumulonimbus clouds with strong convection, so it is often accompanied by strong gusts and heavy rains, and sometimes accompanied by hail and tornadoes. The top of cumulonimbus clouds is generally very high, up to 20 kilometers, and there are often ice crystals on the top of the clouds. The attachment of ice crystals, the breaking of water droplets and air convection make clouds generate charges. The distribution of charge in the cloud is complicated, but generally speaking, the upper part of the cloud is dominated by positive charges and the lower part is dominated by negative charges. Therefore, a potential difference is formed between the upper and lower parts of the cloud. When the potential difference reaches a certain level, discharge will occur, which is our common lightning phenomenon. The average current of lightning is 30,000 amps, and the maximum current can reach 300,000 amps. The voltage of lightning is very high, about 1 billion to 1 billion volts. The power of medium-intensity thunderstorm can reach10 million watts, which is equivalent to the output power of a small nuclear power plant. In the process of discharge, due to the sudden increase of temperature during flashover, the air volume expands rapidly, resulting in shock waves and strong lightning. When the charged Lei Yun is close to the protrusions on the ground, a violent discharge will occur between them. There will be strong flash and explosion roar at the scene of lightning discharge. This is the lightning and thunder that people see and hear.

2. Lu Xun used dozens of pseudonyms in his life. The first time he used the pseudonyms of Lu Xun was his Diary of a Madman. "Lu Xun" means stupid and fast. The signature "Lu Xun" fully expressed his love for his mother and motherland.

I don't know what you mean, just say it briefly.

The global financial crisis of 2007-2009, also known as world financial crisis, subprime mortgage crisis and credit crisis, was named financial tsunami and Wall Street tsunami in 2008, and began to emerge on August 9, 2007. Since the subprime mortgage crisis broke out, investors began to lose confidence in the value of mortgage-backed securities, which triggered a liquidity crisis. Even if many central banks injected huge amounts of money into the financial market many times, they could not stop the outbreak of this financial crisis. Until September 9, 2008, the financial crisis began to get out of control, leading to the closure or takeover of many large financial institutions by the government.