Read the following passage and choose the most suitable from A to G on the list and write it in each gap from 1 to 5.

A. can only be done if astronauts put on their heavy spacesuits

B. and will never be known

C. which is rather more than astronauts really need

D. and are quite noticeable after even a week

E. they start turning somersaults

F. and is vital on very long flights

STAYING HEALTHY IN SPACE

The range of foods available to astronauts is vast, and great care is taken to ensure that it looks and smells appetizing. Meals are organized to provide an average of 3,000 calories a day, which seems high for living in an enclosed environment in which there is no gravity. But astronauts can expend a great deal of energy in doing the simplest things. For example, if they try to turn a handle, they turn themselves as well. If they bend down to do up a shoelace, (1) ________. Finding unusual ways of doing such ordinary things uses up the excess calories. The space diet is balanced rather differently from a terrestrial diet. This is to try and compensate for changes that take place in the body during space flight. Bodily changes begin as soon as astronauts go into space (2) _______________. Among the most serious is calcium loss, which causes a marked reduction in the mass and strength of bones. There is also a progressive loss of red blood cells. What causes these effects is not known, (3) ______________. The heart muscles, with no gravity to battle against, start to waste away. The leg muscles start to waste away too, since walking, as done on Earth, (4) _______________. Exercise also helps to reduce muscle wastage (5) _____________, No one yet knows the limit of human endurance in space. If astronauts can withstand two years or more of continuous weightlessness, the mankind’s dream of visiting other planets could become reality in the early decades of the next century.