Internet Academy

To justify our answer, let's find the information in the text related to each answer choice:

The body works hard under normal gravity.
Text: Most of the article is about microgravity, not normal gravity. But in the fourth paragraph, the writer asks us, "Why should gravity be important? You seldom think about it, but that's just because it's always there. Many of your muscles work against the effects of gravity. So it's no surprise that your body works differently under microgravity." The first part of this paragraph gives basic information about gravity - normal gravity. If muscles work AGAINST the effects of gravity, we can infer they are working hard because we know gravity is a powerful force. The text supports this inference or conclusion. We can't stop here though, even if we think this is the correct answer. Let's be sure to eliminate the other answers.
Gravity has little to do with balance.
Text: We find information about balance and gravity in the fifth paragraph. It says, "One important effect occurs in the body's balancing system. Under microgravity the system gets confused about up and down." We also find out this lack of balance causes space sickness. This information definitely contradicts Answer B.
Microgravity is strongest near Earth's surface.
Text: We find information about where microgravity exists and how strong it is in the third paragraph. The text says "Astronauts in satellites orbiting Earth are living in microgravity -- about a millionth of the gravity at Earth's surface. It's so small that there is no feeling of up or down." This definition tells us that microgravity means "little" gravity where it almost feels like zero gravity and astronauts can't tell what is up or what is down. Near the Earth's surface, we have strong gravity, but not microgravity, by its definition. The opposite of Answer C can be inferred from this information. Answer C is not a correct inference.
People adjust easily to travel in space.
Text: We find several facts to make this statement an incorrect conclusion. The writer says our body works differently under microgravity, we feel negative effects in balancing and in our blood supply system. In addition, muscles can waste away while bones slowly lose calcium, becoming weaker and lighter. These facts indicate the opposite of an easy adjustment for people in space. A reader would draw the conclusion that people have difficulty adjusting to space travel because of the many negative effects. Answer D is not a correct inference.