Change the text below into the passive. In which examples is the person who does it (the agent) not needed?
Scientists in China have discovered an unusual way of predicting earthquakes - snakes! Experts are observing snakes at local snake farms to see if their behaviour changes before an earthquake. The scientists link cameras to a broadband Internet connection. They believe that the snakes can sense earthquakes from 120 km away, three to five days before they happen. They abandon their nests or even smash into walls to escape. Because frequent earthquakes strike China, scientists must find a reliable method of predicting them to avoid the terrible injury and loss of life that