Questions 21 to 23 are based on the following news. At the end of the news item, you will be given 15 seconds to answer the questions. Now, listen to the news. Why did the US break off the diplomatic relations with Iran
A．Iran militants stormed the US Embassy B．Dozens of American hostages were killed in Iran. C．The Iran government refused to give up nuclear experiments. D．The military conflict between the two countries led to the break.