The answer should be C. Teens have higher risk. :))
Traveling, change, and falling in love are all considered good stress. Good stress can turn into bad stress. Good stress can also motivate you and keep you going, but if you no longer feel motivated then the good stress can change to bad stress and cause problems.
The answer is : increased resistance need to be added to the muscles.
Muscle conditioning refer to muscle strength and endurance. In order to improve it, you need to put your muscle in a harsher condition in a harsher condition than it used to be, so your muscle could adjust to it. That's why you should keep increasing the resistance
