题目内容：
Solar Storm At the end of October 2003, a sudden solar storm hit the earth. A solar storm refers to the large amounts of charged particles released into space_______（51） the solar energy increases. The release of the energy_______（52） place along with the activity of the sunspots with a cycle of: 11 years. This time, the_______（53） of the storm exceeded expectations.This_______（54） of intense solar storm was caused by the eruption of a solar flare （闪光） and the ejection （喷发） of the solar corona （日冠） on October 28, 2003. Large amounts of charged particles moved 150,000,000 kilometers through space toward the_______（55） in 19 hours. They could affect aircraft roaming （漫游） in space.
The high-energy particles will_______（56） some of the parts of an aircraft. They may also cause it to fail. High-energy particles can threaten the safety of an aircraft at a high orbit. If an aircraft orbits at a lower orbit, it is_______ （57） because it is under the protection of the earth's magnetic field.
A solar storm not only affects aircraft but also is a _______（58） to the environment and humans. The aerosphere and magnetic field of the earth can_______（59） humans from ultraviolet radiation and X-rays. While most of the X-rays
are absorbed after they enter the aerosphere （大气层）, still a few can_______（60） the ground.
The geomagnetic storm caused by this round of solar storm reaches its highest level on the two_______（61） of the earth, which affects electricity supply of North America. Overexposure to_______（62） threatens the health of passengers on planes flying over the Polar Regions. If we fly in the sky during such a solar storm, it （63） we receive ten times the X-ray radiation. It's really damaging.
Scientists say a solar eruption is like the sun sneezing, which will make the earth_______（64） a cold. Though this natural force is irresistible, scientists can still_______（65） its movement accurately by monitoring. Facing successive solar storms, humans can't drop their guard A．since
B．when
C．until
D．though
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