If you're ever apart from your children, a new study says just talking on the phone will help just as much as a hug  . If you're a parent who spends long hours on the job, you probably feel sorry for spending so much time away from your kids. But the results of a new study show that a mother's voice alone can be just as comforting to an anxious   child as physical contact  . In an experiment, researchers from the University of Wisconsin-Madison asked a group of girls between the age of 7 and 12 to solve math problems in front of judges --- a stressful   situation for anyone. Before the girls were set to solve math problems, the researchers measured their levels of two hormones  : cortisol, which goes up during stressful periods, and oxytocin, the "love" hormone. After they were finished, some of the girls got to meet up with their mothers right away. The mums came in and hugged the girls. Another group of the girls didn't see their mothers, but received phone calls from them, in which their mothers told them how well they'd done. The final group had no contact with their mothers, but watched an animal movie, March of the Penguins instead. Finally, the girls' hormone levels were measured again. Although the movie was interesting, it did nothing to ease   the children's anxiety   ---- but, surprisingly, both the physical contact and phone calls from their mothers had the same effect on easing the girls' stress levels. So, no matter how old you are, if you're feeling stressed about something in your life, a phone call to Mom might be just the key to help you feel better. According to the passage, we can infer that   _  .
it is easy for girls to solve math problems the girls who had watched the movie remained anxious mothers should hug their kids as often as possible older girls have higher cortisol than younger ones.