Read the following passage and write the letter A, B, C or D to indicate the correct answer to each question.

Cycling which can help to increase your strength and energy is one of the best forms of exercise. It makes your muscles and heart stronger. Cycling not only improves your strength but it also a good form of exercise for people with painful feet or back because they do not have to carry the weight of their body on their feet. However, with all forms of exercise, it's important to start slowly and build up gently. Doing exercise too much and too quickly can damage muscles that aren’t used to working so hard. If you have and doubt about taking up cycling to stay healthier, talk to your doctor and ask for his/ her advice. Ideally, you should cycle at least two or three times a week. To do live exercise well, you should practise breathing properly. If you begin to lose your breath, you may think that there is something wrong with your heart and it could be dangerous. Don't worry about that because the shortness of breath shows that the exercise is having the sight effect. However, if you feel you ore in severe pain, you should stop and take a rest.

People with back problems might go cycling because ______.