阅读短文，下列问题
A
June came and the hottest month of the year began. A lot of travelers came to the city by the sea. All of the hotels were full except Mr Johnson's. The prices of all the rooms were the lowest in the city but few people stayed there. The fire (火灾) broke out three times in a year and four travelers died in the accidents. Most workers left there and found jobs in other hotels. Mr Johnson had to do most work himself.
It was eleven o'clock. Most rooms were still empty. Mr Johnson worked for the whole day and was very tired. He went to close the gate when a young man came in, with a big bag in his hand.
“What can I do for you, sir?” asked Mr Johnson.
“The cheapest room in your hotel.”
“OK,” said Mr Johnson, “but it’s on the top floor.”
“It doesn't matter. I think you have a lift in your hotel.”
“Of course, sir,” said the manager. “It’ll take you right there. By the way, may I keep your bag for you?”
“No, thanks. There's nothing expensive in it but a long rope.”
“Oh? What do you bring it with you for?”
“I'm afraid another fire will happen in your hotel. If it does, I'll throw the rope out of the window so that I'll be able to escape from (逃脱）it.”
“Yes?” Mr Johnson said in surprise. “So you have to pay for the bill before you go to your room.”
四种元素中只有一种是金属，下列说法错误的是（ ）