Humans are well-equipped for life on Earth. But in space, it is different. Low or _ changes how the blood flows and causes motion sickness, muscle loss and tiredness. Weightlessness can also cause bone loss. But scientists are experimenting with little worms to better understand how space travel affects astronauts. The millimeter-long worm is called C. elegans. The see-through worm is often used in medical studies because its life is only about two weeks long. Seventy percent of its DNA is the same as human DNA. Sabanayagam is a scientist, who built a micro-gravity simulator to test how C. elegans would perform in the actual zero gravity of space. Scientists put the worms into the simiulator full of water. After a week they take out the worms. They look for changes in the worms' epigenome,which are chemical markers that tell the DNA in the cells how to perform. The epigenome can be changed by the environment. And those changes pass from one generation of worms to the next. "When the worms are in a liquid environment, some epigenomic marks remain even when we take the animal out of the liquid environment and put it back into normal ground conditions. So its offspring keeps this epigenomic memory of the parents' liquid environment or microgravity environment." The information the scientists have gathered suggests that the epigenomic marks appear during the early part of a worm's life. Mr. Sabanayagam says he thinks scientists can find genes in the human similar to those in the worms that responded to microgravity and scientists could possibly observe those genes closely when astronauts travel in space. Sabanayagam expects C. elegans to visit the International Space Station within two years. He says he hopes information gathered from the worm studies can be used to develop simple, low-cost and quick tests to measure an astronaut's health. From the passage we can know C. elegans   _  .
has exactly the same DNA as human is harmful to human is often used in agricultural research has a short life period
Question: Humans are well-equipped for life on Earth. But in space, it is different. Low or _ changes how the blood flows and causes motion sickness, muscle loss and tiredness. Weightlessness can also cause bone loss. But scientists are experimenting with little worms to better understand how space travel affects astronauts. The millimeter-long worm is called C. elegans. The see-through worm is often used in medical studies because its life is only about two weeks long. Seventy percent of its DNA is the same as human DNA. Sabanayagam is a scientist, who built a micro-gravity simulator to test how C. elegans would perform in the actual zero gravity of space. Scientists put the worms into the simiulator full of water. After a week they take out the worms. They look for changes in the worms' epigenome,which are chemical markers that tell the DNA in the cells how to perform. The epigenome can be changed by the environment. And those changes pass from one generation of worms to the next. "When the worms are in a liquid environment, some epigenomic marks remain even when we take the animal out of the liquid environment and put it back into normal ground conditions. So its offspring keeps this epigenomic memory of the parents' liquid environment or microgravity environment." The information the scientists have gathered suggests that the epigenomic marks appear during the early part of a worm's life. Mr. Sabanayagam says he thinks scientists can find genes in the human similar to those in the worms that responded to microgravity and scientists could possibly observe those genes closely when astronauts travel in space. Sabanayagam expects C. elegans to visit the International Space Station within two years. He says he hopes information gathered from the worm studies can be used to develop simple, low-cost and quick tests to measure an astronaut's health. From the passage we can know C. elegans   _  .
A. has exactly the same DNA as human
B. is harmful to human
C. is often used in agricultural research
D. has a short life period
Answer: