Read the excerpt from "Exploring Mars.”
The most famous strange sighting took place in 1976. After a ten-month trip, the Viking I spacecraft reached Mars. The Viking I went into orbit around the planet. It took photos of the surface and sent them to Earth.
Which sentence from the excerpt best expresses the central idea?
The most famous strange sighting took place in 1976.
After a ten-month trip, the Viking I spacecraft reached Mars.
The Viking I went into orbit around the planet.
It took photos of the surface and sent them to Earth.