Questions 21 and 22 are based on the following news. At the end of the news item, you will be given 10 seconds to answer the questions.
Now, listen to the news.
How many members are there in the Arab League

A．How to care for precious metals.
B．A standard unit for measuring weight.
C．The value of precious metals.
D．Using the metric system.

A．help mariners.
B．improve ship design and sailing method.
C．study astronomy and mathematics.
D．improve his own skill as a sailor.