In 1784, the famous astronomer William Herschel wrote that the dark areas on the surface of Mars are the oceans, while the brighter areas are the land. Herschel speculated that there must be intelligent life on Mars, and they may be related to our earth people. Almost. Herschel's theory has been popular for more than a century, and even some other astronomers have agreed that vegetation can be observed in some brighter areas. If the following are true, which one best supports Herschel's conjecture? ['Where intelligent life exists, there must be ocean and land.', 'Where there is vegetation, there must be intelligent life.', 'Where there is an ocean, there must be an intelligent life on the land.', 'Smart life may exist where vegetation can be observed.']