Read the following article and answer the question. Article: Cyril was a small town. The houses there were all made of wood; almost everything in the houses such as cupboards, tables and chairs were made of wood, too. And all the houses faced south. The town was never peaceful. Fire broke out once a week on summer afternoons. Residents were puzzled who the real firebug was. One day a big fire broke out. It was said that a Negro had jumped out of the house on fire, so the police arrested all the Negroes in the street. However, fire never stopped to breaking out when the Negroes were in prison. Mauson, a physics teacher didn't believe that the Negroes were the firebugs, for he really knew about those Negroes, He made up his mind to find out who the real firebug was. One day he was invited to drink in a pub and happened to notice that many bottles and plastic plates were baked by the hot sunrays. Suddenly he realized what the actual fact was. He jumped with joy, saying, "I've got the answer!" Mauson dashed out of the pub to his friend's house nearby, which also faced south. He made an experiment there to confirm his idea. The next Saturday afternoon, Mauson asked some policemen and newsmen to come to the house. They were told that the real firebug would be shown there. At that time the sun was shining full into the house and it became hotter and hotter inside the room. Someone wanted to draw the curtains together, while another was going to use a bottle to drink water, but neither got permission from Mauson, who wanted to let the firebug in. "Now," said Mauson, "this house will soon catch fire." People looked at each other in surprise. Mauson asked them to look at the bottles and focus on the table cloth. After a while the cloth gave off a burning smell and began to catch fire! The mystery of fire was discovered, but the police wouldn't believe him and insisted that Negroes had been the firebugs. Instead they arrested Mauson and put him into prison. But Mauson said he would never turn against science. Question: Drinking in a pub, Mauson realized what the actual fact was _ . Answer:
Options are: 1. by experiment. 2. by backing the bottles. 3. through the hot sunrays. 4. by accident.
4.