Mothers can still offer comfort, even from a distance, a new study has found. The results show that simply hearing their mothers' voice over the phone works just as well at calming the nerves of stressed children as a real-life pat on the shoulder. The soothing effect is most likely due to the release of the hormone , oxytocin , in the brain, the researchers say. This "love hormone" is known to _ stress and is likely to be involved in social connections, including those between a mother and a child. Previous work has revealed that this hormone is released during physical contact with a mother. "But it's clear from these results that a mother's voice can have the same effect as a hug, even if she isn't actually standing there," said the researcher, Leslie Seltzer, a biological scientist. Seltzer tested a group of 61 girls, aged 7 to 12, by having them make an unprepared speech and solve a series of maths problems in front of a group of strangers, sending their hearts racing and levels of cortisol--a hormone associated with stress--soaring. Facing a challenge like that raises stress levels of a lot of people. Once stressed, a third of the girls were comforted in person by their mothers with hugs. A third of the girls watched an emotionally neutral 75-minute video. The rest were handed a telephone with their mothers on the line. For the girls who interacted in person or over the phone with their mothers, the levels of the "love hormone" rose significantly, and the stress-marking hormone was washed away. This effect didn't show up for participants who watched the video. Seltzer is now testing the amount of oxytocin released with other communication methods--like text messaging--and hopes to see the research spread out from human subjects. "It's not just us, of course. Lots of very social species have voices," she said. "on the one hand, we are curious to see if this effect is unique to humans. On the other, we're hoping researchers who study vocal communication will consider looking at oxytocin release in other animals and apply it to broader questions of social behavior and evolutionary biology. Mothers' voice over the phone can reduce children's nerves according to the study, because  _  .
children can imagine their mothers' hugs on the line children enjoy their mothers' voice and forget their worries mothers are good at comforting their children, even on the phone mothers' voice can promote the release of the love hormone
Question: Mothers can still offer comfort, even from a distance, a new study has found. The results show that simply hearing their mothers' voice over the phone works just as well at calming the nerves of stressed children as a real-life pat on the shoulder. The soothing effect is most likely due to the release of the hormone , oxytocin , in the brain, the researchers say. This "love hormone" is known to _ stress and is likely to be involved in social connections, including those between a mother and a child. Previous work has revealed that this hormone is released during physical contact with a mother. "But it's clear from these results that a mother's voice can have the same effect as a hug, even if she isn't actually standing there," said the researcher, Leslie Seltzer, a biological scientist. Seltzer tested a group of 61 girls, aged 7 to 12, by having them make an unprepared speech and solve a series of maths problems in front of a group of strangers, sending their hearts racing and levels of cortisol--a hormone associated with stress--soaring. Facing a challenge like that raises stress levels of a lot of people. Once stressed, a third of the girls were comforted in person by their mothers with hugs. A third of the girls watched an emotionally neutral 75-minute video. The rest were handed a telephone with their mothers on the line. For the girls who interacted in person or over the phone with their mothers, the levels of the "love hormone" rose significantly, and the stress-marking hormone was washed away. This effect didn't show up for participants who watched the video. Seltzer is now testing the amount of oxytocin released with other communication methods--like text messaging--and hopes to see the research spread out from human subjects. "It's not just us, of course. Lots of very social species have voices," she said. "on the one hand, we are curious to see if this effect is unique to humans. On the other, we're hoping researchers who study vocal communication will consider looking at oxytocin release in other animals and apply it to broader questions of social behavior and evolutionary biology. Mothers' voice over the phone can reduce children's nerves according to the study, because  _  .
A. children can imagine their mothers' hugs on the line
B. children enjoy their mothers' voice and forget their worries
C. mothers are good at comforting their children, even on the phone
D. mothers' voice can promote the release of the love hormone
Answer: