The Legend of Toba Lake There was a handsome man named Batara Guru Sahala, who enjoyed fishing so much. One day he caught a fish. He was surprised to find out that the fish could talk. The fish begged him to set it free. Batara Guru Sahala could not bear it. He made the fish free. As soon as it was free, the fish changed into a very beautiful woman. Batara Guru Sahala fell in love with that fish-woman and wanted to marry her. Batara Guru Sahala promised to keep the secret that she had been a fish and would never tell anybody about it. They were married happily. They had two daughters. One day Batara guru Sahala got very angry with his daughters. He could not control his temper. He shouted angrily and got the word of fish to his daughters. The daughters were crying. They found their mother and told her about it. The mother was very angry. Batara Guru Sahala broke his promise. The mother was shouting angrily, then the earth began to shake. Volcanoes started to erupt. The earth formed a very big hole. People believed that the big hole became a lake. Today the lake is known as Toba Lake. What is the main idea of the fourth paragraph?

The Legend of Toba Lake
          There was a handsome man named Batara Guru Sahala, who enjoyed fishing so much. One day he caught a fish. He was surprised to find out that the fish could talk. The fish begged him to set it free.
          Batara Guru Sahala could not bear it. He made the fish free. As soon as it was free, the fish changed into a very beautiful woman. Batara Guru Sahala fell in love with that fish-woman and wanted to marry her. Batara Guru Sahala promised to keep the secret that she had been a fish and would never tell anybody about it.
          They were married happily. They had two daughters. One day Batara guru Sahala got very angry with his daughters. He could not control his temper. He shouted angrily and got the word of fish to his daughters. The daughters were crying. They found their mother and told her about it.
          The mother was very angry. Batara Guru Sahala broke his promise. The mother was shouting angrily, then the earth began to shake. Volcanoes started to erupt. The earth formed a very big hole. People believed that the big hole became a lake. Today the lake is known as Toba Lake.

What is the main idea of the fourth paragraph?