Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.

As viewed from space, 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 toharborlife.Circlingthe Sun at an average distance of149 million kilometers (93 million miles), Earth is the third planet from the Sun and the fifth largest planet in the solar system.

Our planet’s rapid spin and molten nickel-iron core give rise to an extensive magnetic field which, coupled the atmosphere, shields us from nearly all of the harmful radiation coming from the Sun and other stars. Earth’s atmosphere protects us from meteors as well, most of which burn up in the Earth’s atmosphere before they can strike the surface. The planet active geological processes have left no evidence of the ancient pelting it almost certainly received soon after it formed about 4.6 billion years ago. The Earth has a single natural satellite – the moon.

Approximately how much of the Earth’s atmosphere is nitrogen?