“Tiny drops of water could collect inside,” he said. “If there are gases coming out, they could provide energy for a whole range of bacteria. A cave is also a protection from radiation; the surface of Mars is exposed to high levels of space radiation.
The caves probably formed when tube-shaped lava flows(管状岩浆流) spread across the planet long ago. The outside of the tubes cooled,forming solid walls, while something hotter inside allowed the remaining lava to flow out, forming caves.”
1. What does the passage mainly talk about?
A. How the caves were formed on Mars.
B. How scientists found these caves on Mars.
C. Caves on Mars may be full of hot air or a sign of life.
D. Scientists have completely recognized the surface of Mars.
2. We can learn from the passage that .
A. water has already been found on Mars
B. the scientists found all the caves at night
C. it is certain that there is life in these caves
D. the surface of Mars is bitterly cold,radiation-soaked and dry
