As viewed from space, the Earth’s distinguishing characteristics are its blue waters and white clouds. Enveloped by an ocean of

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问题     As viewed from space, the Earth’s distinguishing characteristics are its blue waters and white clouds. Enveloped by an ocean of air consisting of 78% nitrogen and 21% oxygen, the planet is the only one in our solar system known to harbor life. Circling the Sun at an average distance of 149 million km (93 million miles), the Earth is the third planet from the Sun and the fifth largest planet in the solar system. Its rapid spin and molten nickel-iron core give rise to an extensive magnetic field which, coupled with the atmosphere, shields us from nearly all of the harmful radiation coming from the Sun and other stars. Most meteors burn up in the Earth’s atmosphere before they can strike the surface. The planet’s active geological processes have left no evidence of the ancient pelting it almost certainly received soon after it was formed. The Earth has a single natural satellite -- the Moon.
What two factors help protect the Earth from radiation?

选项 A、Magnetic field and atmosphere.
B、Rapid spin and molten iron-nickel core.
C、The Sun and the Moon.
D、Blue waters and white clouds.

答案A

解析 见文中第四句:Its rapid spin and molten nickel-iron core give rise to an extensive magnetic field which,coupled with the atmosphere,shields us from nearly all of the harmful radiation coming from the Sun and other stars.地球快速的自转以及其熔融的镍铁地核引发了广泛的磁场,再加上大气层,保护我们免受来自太阳及其他星体的几乎所有的有害辐射。由此我们得出:帮助地球免受辐射的两个因素是A.“磁场和大气层”。
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