Reading 8 Read an article about the giant concrete arrows that have been found in the USA. Match sentences A-G with gaps 1-5. There are two extra sentences.

Follow the arrow

If you have even been inside the cockpit of a plane, you will have noticed the large number of instruments on the walls and ceiling around the pilot's seat Unlike car drivers, pilots do not have the luxury of signs and arrows telling them where to go. Instead, they rely on sophisticated GPS systems. So how were pilots able to find their way in the days before radio and satellite communication?

In the USA, the problem of navigation first arose when the airmail postal service was introduced in 1911. In the beginning, huge bonfires were Iit to show pilots where to land in the dark. Later, a more practical solution was found: the construction of giant concrete arrows on the ground. To enable pilots to see them at night, a steel tower with lights was built in the middle. The top light turned around to attract the pilot's attention, and two others lit up the arrow and flashed a code to identify its location.

The first of these arrows was laid in 1924, and by 1929, there were around 1,500 of them. 3 The arrows were spaced about 16 km apart and were an important part of the Transcontinental Airway System. But by the 1940s, new navigation techniques were being discovered and soon, the arrows and their towers were no longer needed. They were gradually abandoned and some of them were removed completely.

However, not all of the arrows have disappeared. Some are still visible in the empty areas of other states such as Utah, Wyoming and Indiana. Yet, either because of their size or due to their bad condition, the arrows are not easy to find. In many cases, if you want to see one, it is a question of knowing where to look.

Which is where retired couple Brian and Charlotte Smith can help. The two are devoted fans of the arrows and spend much of their time hunting them down. Once they find an arrow. they map its location, photograph it and upload the details onto their website. Their aim is to preserve the memory of these historical structures and prevent them from being lost forever.

A They formed an illuminated path for airmail pilots stretching from New York to San Francisco.

B Plans were made for a floating version that would cross the Atlantic Ocean.
C Many of these buttons, dials and screens are used in navigation.
D So far, they have located more than a hundred of them.
E In the state of Montana, they are still used for guiding pilots through the mountains.
F When hikers come across them, they often wonder why they were built.
G The arrows were 21 m long and painted bright yellow.