The moment the spacecraft is sent，the speed is extremely fast.Your body feels four times its normal weight.When you are pushed back into the seat，moving your arms is increasingly difficult.Some astronauts may even become unconscious."Gravity(重力)pushes blood into the feet and we need blood supply(供血)to our brain to stay conscious，"explained Jon Scott，a space scientist.

　　T­plus 10 minutes：Nausea(恶心)

　　One of the first things that astronauts complain about is nausea or sickness.This effect of the lack of gravity on the inner car influences balance.It also influences the piloting skills.

　　T­plus two days：A swollen(肿胀的)face

　　Being in space is like standing on your head；the water in your body is likely to gather in the upper part of your body，giving you a swollen face.But this is the least of your problems.A recent study also suggests that lack of gravity can lead to bad eyesight.

　　T­plus one week：Muscle and bone loss

　　With the gravity gone，your body would go worse.A lot of the body's systems depend upon gravity to keep them conditioned.In some experiments with rats，up to a third of muscle from particular muscle groups was lost within 7 to 10 days of space flight.And while it is not a problem when you are flying around in the International Space Station(ISS)，it's a great concern if you plan to land on Mars，200 million kilometers from home，unable to walk.

　　Lack of gravity also causes bone to be lost.For future Mars walkers，this is bad news.Imagine if one small step for mankind were to result in a broken leg.

　　【语篇解读】　本文介绍了太空旅行对人体所造成的影响。

　　1．What is the main idea of the passage?

　　A．The influences of space travel on the human body.

　　B．The reasons for human beings landing on Mars.

　　C．The solutions to the problems during space travel.

　　D．Humans' progress in the space program.

A　[主旨大意题。根据第一段"The following are influences on the human body."可知本文主要介绍了太空旅行对人体的影响。]