​If you are young now and want to avoid developing osteoporosis when you are older, which kind of exercise would be most effective?

A) ​Swimming laps
B) ​Jumping rope
C) ​Walking
D) ​Tai chi

Weight-bearing exercises like jumping rope have been shown to be the most effective in building bone density and preventing osteoporosis. Swimming and tai chi are not weight-bearing exercises, and while walking is beneficial for overall health, it may not be enough to significantly build and maintain bone mass.