[听力原文]11-15

Thirteen has long been considered as an unlucky number by many Westerners who tried their best to avoid any connections to it. But some people are indifferent to it and the results proved not to be as dangerous as people thought.

Born on Oct. 13, 1925, Margaret Thatcher got married on Dec. 13, 1951. Exactly 3 years after the marriage, that is, Dec. 13, 1954, Margaret gave birth to a boy and a girl. Her son got engaged on Nov. 13, 1986 when he was 32 years old. That year also marked the 35th anniversary of the Thatcher couple’s marriage. Many great activities were held on Dec. 13 to celebrate the time of their marriage.

What’s the main idea of the passage
The number 13 is（）as people once thought.