Last Sunday I saw the worst storm in years. It came suddenly and went on for more than three hours. After lunch, I went into my room to have a rest. The air was hot, and all was quiet.The strong wind started blowing into my room. Pieces of paper on my desk flew high into the air and some flew out of the open window. As I ran out to catch them, big drops of rain began to fall. When I came back into the house, it was raining harder and harder. I tried very hard to close the window. Then I heard a loud crashing sound from the back of the house. I ran out of my room to find out what it was--- a big tree had fallen down and broke the top of the back room. The top of the back room was broken because of   _  .
the hot air the crashing sound the rain the falling tree