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【单选题】Unless we spend money to spot and prevent asteroids (小行星) now, one might crash into Earth and destroy life as we know it, say some scientists. Asteroids are bigger versions of the meteoroids (流星) that...
A.
It is very unlikely, but the danger exists.,
B.
Such a collision might occur once every 25 years.
C.
Collisions of smaller asteroids with Earth occur more often than expected.
D.
It’s still too early to say whether such a collision might occur.
【单选题】Space is a dangerous place, not only because of meteors (流星) but also because of rays from the sun and other stars. The atmosphere again acts (67) our protective blanket on (68) . Light gets through, ...
A.
from
B.
than
C.
as
D.
away
【单选题】Space is a dangerous place, not only because of meteors (流星) but also because of rays from the sun and other stars．The atmosphere again acts 【C1】______ our protective blanket on 【C2】______ ．Light gets...
A.
for
B.
with
C.
on
D.
as
【单选题】Space is a dangerous place, not only because of meteors(流星) but also because of rays from the sun and other stars. The atmosphere again acts as our protective blanket on earth. Light gets through, and...
A.
The Atmosphere and Our Environment
B.
Research on Radiation
C.
Effects of Space Radiation
D.
Importance of Protection Against Radiation