What was your favorite sport during your childhood? Maybe running around the playground or jumping rope for hours would bring you pleasure. At that time you weren't thinking of health, you were just thinking of entertainment . But in this age of high-tech home equipment, the simple joy of jumping rope has been forgotten. I think rediscovering it probably will give you a total-body exercise. Although considered an excellent form of exercise, jumping rope has never been widely accepted because of two reasons. First, most people consider jumping rope to be an excellent form of cardiovascular   exercise, but they also believe that it is simply too difficult. In other words, they don't think they'll be able to continue jumping for the near 20 minutes in order to achieve a beneficial physical effect. Second, many  people regard it as a little boring and overly repetitive --not as something fun or enjoyable.  _ . Instead of doing the usual two-foot bounce  over and over again, players good at rope-jumping often change their pattern every 10 or 20 jumps. A single bounce, a double -bounce, a skip, a knee-up, side swings, as well as a variety of other easy-to-learn free-style rope-jumping . Nowadays researchers are discovering that jumping rope also prepares the brain for learning. It is an exercise allowing both brain hemispheres to perform equally to each other . In a word, jumping rope can be a life-long activity requiring little equipment, time and space, yet leading to a much healthier life. According to the researchers, jumping rope  _  .
only prepares the brain for learning is suitable for students only helps both brain hemispheres work together can be dangerous for old people
Question: What was your favorite sport during your childhood? Maybe running around the playground or jumping rope for hours would bring you pleasure. At that time you weren't thinking of health, you were just thinking of entertainment . But in this age of high-tech home equipment, the simple joy of jumping rope has been forgotten. I think rediscovering it probably will give you a total-body exercise. Although considered an excellent form of exercise, jumping rope has never been widely accepted because of two reasons. First, most people consider jumping rope to be an excellent form of cardiovascular   exercise, but they also believe that it is simply too difficult. In other words, they don't think they'll be able to continue jumping for the near 20 minutes in order to achieve a beneficial physical effect. Second, many  people regard it as a little boring and overly repetitive --not as something fun or enjoyable.  _ . Instead of doing the usual two-foot bounce  over and over again, players good at rope-jumping often change their pattern every 10 or 20 jumps. A single bounce, a double -bounce, a skip, a knee-up, side swings, as well as a variety of other easy-to-learn free-style rope-jumping . Nowadays researchers are discovering that jumping rope also prepares the brain for learning. It is an exercise allowing both brain hemispheres to perform equally to each other . In a word, jumping rope can be a life-long activity requiring little equipment, time and space, yet leading to a much healthier life. According to the researchers, jumping rope  _  .
A. only prepares the brain for learning
B. is suitable for students only
C. helps both brain hemispheres work together
D. can be dangerous for old people
Answer: