The vast jungles of the Amazon rainforest are home to tribes(部落)mostly isolated(隔绝的)from the outside world，whose way of life，largely unchanged for hundreds of years，is now increasingly threatened by modern civilization．
Now, scientists discover they can monitor these“uncontacted tribes”using satellites，which would allow inexpensive and safe tracking of these tribes in order to protect them from outside threats．
In order to help conserve these uncontacted Indians，researchers need accurate estimates of their populations．One way to collect this data involves flying over their villages，but such overflights are both expensive and could fill these native peoples with fear．Another strategy involves meeting individuals on the ground，but among other risks，scientists could accidentally spread disease to members of the tribes．
Instead，scientists investigated whether satellite imaging could monitor uncontacted tribes. The result was inspiring．They confirmed their locations and measured the sizes of their Village，houses and gardens．“We can find isolated vinages with remote sensing and study them over time．”Walker told Live Science．“We can ask：Are they growing?Do they move?”
Surprisingly，based on the sizes of the houses and Villages，the scientists find the population densities of these isolated villages are about 10 times greater，on average，than other villages of native Brazilian peoples．This may be due to the fact that they have to live closer together because they are not as good at clearing the forest，since they lack modern devices like chainsaws and tractors，the researchers said．The tribes may also be afraid of spreading out due to fear of being attacked by outsiders，Walker said.
The researchers now plan to focus on 29 more isolated villages to“look at their ecology—that is．distance from rivers and roads—and use this to model where else we can find more isolated villages，”Walker said．
What is the main idea of the text?

A．Amazon tribes are disappearing．

B．Scientists found isolated Amazon tribes．

C．Modern civilization is threatening Amazon tribes．

D．Isolated Amazon tribes are monitored with satellites．

Scientists don't want to meet the Indians on the ground due to the fear that_______

A．they can’t get accurate data

B．they will be attacked by the Indians

C．they could pass disease to the Indians

D．they will catch disease from the Indians

What do scientists find about the tribes?

A．They live close together．

B．Their population is dropping.

C．Thev live in distributed areas．

D．Their population is increasing fast.

What can be inferred from the last paragraph?

A．There are 29 Amazon tribes in total．

B．More isolated tribes are yet to be discovered．

C．It's easy for scientists to find isolated villages．

D．Isolated villages are distant from rivers and roads．