Questions 17 to 20 are based on the following passage. At the end of the passage, you will be given 20 seconds to answer the questions.
Now listen to the passage.

Why was the speed limit first reduced to 55 miles-per-hour

A．The older people wanted it.

B．The voters decided on it.

C．It was decided that speeds above that were not safe.

D．The US had a fuel crisis.

位于后纵隔脊柱旁肋脊区内最常见的纵隔肿瘤是（）

A.胸腺瘤

B.心包囊肿

C.畸胎瘤

D.神经源性肿瘤

E.淋巴瘤