Read the passage and answer the questions that
THE RED PLANET
Do you know there are many planets in our solar system and one of them is referred as 'the red planet'? This fourth planet from the sun, which is reddish in colour, is Mars. Mars gets its reddish colour from the high amount of iron oxide on its surface.
Mars is also home to Olympus Mons, the highest discovered mountain in the solar system. With its peak at 88,600 feet, Olympus Mons is about three times as high as Mount Everest, which is 29,029 feet, the highest peak on Earth. Mars' Valles Marineris is the solar system's largest canyon, measuring more than seven miles deep.
Of all the planets, temperatures on Mars are most similar to those on Earth. Unlike Earth, however, the thin atmosphere gives rise to fearsome dust storms that may envelop the entire planet and cause overall temperatures to rise. Mars has an extremely thin atmosphere.
95% of it is carbon dioxide, 3% is nitrogen, 1.6% is argon, and the remainder consists of traces of oxygen and water. Mars has two moons, Phobos and Deimos. Interestingly, Phobos orbits Mars at a distance of only about 5,500 miles from its center, the closest any moon orbits its parent planet. Because Phobos has a particularly low orbit, scientists believe it will eventually crash into Mars or break up into pieces, possibly forming rings around the planet like Saturn.
There has long been speculation concerning the possibility of life and of liquid water on Mars. Some evidence on the planet's surface suggests the presence of liquid water at some point in history, but scientists think this water would be too salty or acidic to support life. There is compelling evidence, however, that Mars was once much more habitable to life than it is today.
Many spacecraft have attempted to visit Mars, the most notable of which was NASA's Mariner 4, the first to visit in a fly-by in 1965. In 1976, Viking 1 and 2 became the first spacecrafts to conduct successful and sustained landings on Mars. They provided the first colour photographs of the "red planet". In May of 2008, the NASA Phoenix lander touched down on the north polar region of Mars to study surface features.
______ was the first spacecraft to have sustained landing on Mars.
the answer is d