Answer: Q1 - To stretch before the practice, do not exceed yourself while doing it, keep hydrated and follow your workout program with the help of a professional.
Q2- DOMS is when you feel pain in your body after exercising, mainly because you weren't used to the intensity of it. It is caused by rips in your muscles and can be treated by R.I.C.E treatments.
Q3- R.I.C.E consists in resting, icing, compressing and elevating the body part you feel pain in. It helps you to recover from excessive physical activity.
Q4- The difference is where the sprain and strain happen. Strains happen in muscles or tendons, and sprains happen in ligaments. Also, sprains depend on their extent, while strains on their severity.
Q5- Heat exhaustion is caused by severe dehydration while sweating and not hydrating anymore. Heat stroke happens due to the increase of the body temperature in a very short period of time. Both can result in unconciousness for the victim.
Q6- You should change it because otherwise your muscles will get used to the same physical activity and won't be developing anymore after the given period. By changing workouts, you can increase their performance, by for example praticing different activities that stimulate you in different ways.