Questão 2555693

Read the text and answer questions 28, 29 and 30.

Twenty-First Century Birdwatching

1 Our ancestors could spot natural predators from far by

their silhouettes. Are we equally aware of the predators in the

present-day? Drones are remote-controlled planes that can be

used for anything from surveillance, to rescue operations and

5 scientific research. Most drones are used today by military

powers for remote-controlled surveillance and attack, and

their numbers are growing. The Federal Aviation

Administration (FAA) predicted in 2012 that within 20 years

there could be as many as 30.000 drones flying over U.S. Soil

10 alone. As robotic birds will become commonplace in the near

future, we should be prepared to identify them.

(Adapted from https://medium.com/looking-up/21st-century-birdwatching)

“Their”, (line 7), underlined in the text, refers to