1 . During space missions, astronauts can experience a loss of some of the inner structural support in their bones. For trips in space lasting at least six months, that loss is equal to about 20 years of aging. Luckily, a new study finds a year back on Earth rebuilds half of the strength lost in the affected bone.

Exercise scientist Leigh Gabel was part of a team that tracked 17 astronauts, each of whom had spent four to seven months in space. The team measured the 3-D structure of bone. They focused on the structure of the tibia (胫骨) and the lower-arm bone. The researchers took images of the bones 3 times—before spaceflight and again six months and one year later when the astronaut s returned home from space. From these pictures, Gabel’s team calculated an astronaut’s bone strength and density (密度) at each of those times.

What did they find through comparison of the pictures? Astronauts in space for less than six months regained their preflight bone strength after a year back on Earth. But those who stayed in space longer suffered permanent hone loss in their tibias. That loss was equal to a decade of aging. The lower-arm bones showed almost no loss. That was likely because these aren’t weight-bearing hones on Earth, Gabel explains. In fact, those arms can get a bigger workout in space than on Earth as astronauts use them to move around their craft by pushing off handles and doors.

“Inereasing weight-lifting exercises in space could help alleviate (缓解) bone loss in the legs,” says Steven Boyd, also in exercise scientist.

“With longer spaceflight, we can expect bigger bone loss—and probably a bigger problem with recovery,” says physiologist Laurence Vico. “Space agencies should also consider other bone health measures, such as nutrition, to reduce bone loss and increase bone formation.”

1. Why did Gabel’s team take pictures at different times?

A．To offer evidence for their predictions.

B．To show their respect for the astronauts.

C．To compare the changes in the astronauts’ bones.

D．To find out the proper length of staying in space for astronauts.

2. Which of the following may Gabel agree with?

A．A spaceflight in less than half a year does no harm to astronauts.

B．Astronauts coming back from a spaceflight look much older.

C．Astronauts can avoid bone loss through doing enough exercise.

D．There is almost no difference in the astronauts’ lower-arm bones.

3. What can we conclude from this text?

A．People on Earth never suffer bone loss.

B．The finding of the new study is good news for astronauts.

C．The 17 astronauts knew the bone loss before their spaceflights.

D．Astronauts can regain their bone strength as soon as they return to Earth.

4. What does the text mainly talk about?

A．How to prevent bone loss in space.

B．Problems faced by astronauts in space.

C．Astronauts’ suffering from bone loss in space.

D．Astronauts’ contributions to the development of science.