Life on Mars could become a reality and it could happen in your lifetime. A welcoming planet Scientists say Earth's neighbor Mars, a bright red planet about half Earth's size, is the most likely to support human life. Mars even has frozen water on its surface. Since the late 1990s, NASA has been exploring Mars using remote-controlled vehicles . Most recently Curiosity, a car-size vehicle, traveled through space on an unpiloted spacecraft  and landed on Mars in August 2012. Directed by NASA scientists , the vehicles move on the surface, taking pictures , collecting and analyzing soil, and looking for signs of life. But what about human explorers? Plans are already in the works to send astronauts to Mars as soon as the mid-2030s.  _  But before you start packing your bags, let's consider the challenges. For starters, Mars is far away. Just getting there could take up to 10 months. Scientists already know that time away from Earth's gravity harms the human body. Bones and muscles get weaker. The body produces less blood. What damage would months and months of living in space do? And then there is the matter of water, oxygen, food and fuel. Scientists will have to find solutions to these problems, or the first humans on Mars won't survive very long in their new home. Tiny Dangers There's another tinier risk. It's so tiny that you can't even see it: germs. Some scientists believe that our germs could pollute the whole planet of Mars. Potentially killing Martian life before we have the chance to discover it. Worse, there is a small but terrifying chance that any microscopic life already there might be harmful to us . Worse still, if any of those Martian germs  were brought back to Earth, the result could be disastrous. Animals, plants, and people could be wiped out. Worth the $$$? A more practical concern is the cost. The price could approach $ 1 trillion . How can we justify spending that much when so many problems--poverty, disease--could use the cash here on Earth? By "Tiny dangers" the author means   _  .
there is no serious danger people won't be in any danger it's difficult for people to realize the danger the danger may be caused by very small things
Question: Life on Mars could become a reality and it could happen in your lifetime. A welcoming planet Scientists say Earth's neighbor Mars, a bright red planet about half Earth's size, is the most likely to support human life. Mars even has frozen water on its surface. Since the late 1990s, NASA has been exploring Mars using remote-controlled vehicles . Most recently Curiosity, a car-size vehicle, traveled through space on an unpiloted spacecraft  and landed on Mars in August 2012. Directed by NASA scientists , the vehicles move on the surface, taking pictures , collecting and analyzing soil, and looking for signs of life. But what about human explorers? Plans are already in the works to send astronauts to Mars as soon as the mid-2030s.  _  But before you start packing your bags, let's consider the challenges. For starters, Mars is far away. Just getting there could take up to 10 months. Scientists already know that time away from Earth's gravity harms the human body. Bones and muscles get weaker. The body produces less blood. What damage would months and months of living in space do? And then there is the matter of water, oxygen, food and fuel. Scientists will have to find solutions to these problems, or the first humans on Mars won't survive very long in their new home. Tiny Dangers There's another tinier risk. It's so tiny that you can't even see it: germs. Some scientists believe that our germs could pollute the whole planet of Mars. Potentially killing Martian life before we have the chance to discover it. Worse, there is a small but terrifying chance that any microscopic life already there might be harmful to us . Worse still, if any of those Martian germs  were brought back to Earth, the result could be disastrous. Animals, plants, and people could be wiped out. Worth the $$$? A more practical concern is the cost. The price could approach $ 1 trillion . How can we justify spending that much when so many problems--poverty, disease--could use the cash here on Earth? By "Tiny dangers" the author means   _  .
A. there is no serious danger
B. people won't be in any danger
C. it's difficult for people to realize the danger
D. the danger may be caused by very small things
Answer: