Read the following article and answer the question. Article: Mars Was Not Always Bitterly Cold Scientists at the California Institute of Technology (Caltech) have reported evidence that Mars was warmer and wetter long ago than it is today. The Caltech scientists say they have directly _ the temperature of Mars four billion years ago. At least, they established the surface temperature on part of the planet at that time. The researchers say it is the first such evidence to be discovered and presented. The Caltech scientists say carbonate minerals formed on Mars at about eighteen degrees Celsius. They reached the finding after studying a meteorite that had its beginnings near the Martian surface. Today, the average temperature on Mars is sixty-three degrees below zero Celsius. The finding was reported on the website of the National Academy of Sciences. Caltech Assistant Professor Woody Fischer helped to prepare the report. He says eighteen degrees Celsius is not especially cold or hot. He says this makes the finding extremely interesting. Knowing the temperature can give scientists an idea of the climate on Mars long ago. It can also help them decide whether the planet had liquid water. Spacecraft orbiting Mars have shown what appear to be rivers, lakebeds and mineral deposits. These pictures suggest that, at one time, water did flow there. Mars Rover vehicles and other spacecraft have confirmed the information. Caltech Geology Professor John Eiler was another writer of the report. He says knowing the temperature of Mars from long ago provides valuable information. It shows that early in the planet's history, at least part of Mars could support a climate like that of Earth. The meteorite the scientists examined is one of the oldest known rocks in the world. It is called the Allan Hills meteorite. Its name came from the place in Antarctica where it was found in 1984. The meteorite is believed to have blown loose from the Mars' surface when another space rock struck its "home." Question: How did the scientists reach the finding? Answer:
Possible answers:
a). By studying Allan Hills meteorite.;
b). By using spacecraft orbiting Mars.;
c). By studying minerals gathered on Mars;
d). By studying a meteorite on the Martian surface.;
a).