Question 21 is based on the passage you have just heard

听力原文：

    Have you ever heard of the Vikings? They were sea travelers from Norway. (21) More than a thousand years ago, they made three important geographical discoveries.

    (19) The Vikings’ first major discovery occurred in the ninth century. A man called Naddod was on his way from Norway to the Faroe Island, north of England, when his ship was caught in a storm. The storm blew the ship west for several days. When the weather cleared, Naddod found himself on the coast of a new land. (19) Later, Viking travelers named it Iceland.

    In 982, a Viking called Eric the Red sailed west in search of new land. (20) Five hundred miles west of Iceland, he and his men reached an icy rocky mass of land. They sailed around it until they reached the western side. Here, they found some green areas, so they named the island Greenland.

    Then, in 1001, the Vikings made their most important discovery. The son of Eric the Red, named Leif Ericson, had heard rumors about land west of Greenland. He sailed west and soon found it. He and his men landed in three places. They called the first one Helluland, which means land of flat stones. The Vikings then sailed south and made their second landing. They named this place Markland. Their third landing was at a place they called Vineland. Leif Ericson and his men were the first Europeans to walk on the shores of North America, almost 500 years earlier than Columbus.

21. What does the speaker mainly talk about?

解析：A。本题为主旨题。问题为：说话人主要讲述了什么？原文开头介绍Vikings是航海者，“More than a thousand years ago, they made three important geographical discoveries.”，超过一千年以前，他们做出了3次大地理发现。接着在后面详细讲述了三次发现的详细经过，可见说话人主要在说Vikings的海上探险活动，选项A) The Vikings’ ocean explorations.为正确答案。