Read the text and choose the correct answer. It is imperative to utilize proper techniques of stretching to keep your muscles in good shape. Different stretches are used by professionals. For example, fitness and stretching exercises of professional surfers incorporate dynamic stretches, and professional surfers emphasise on relaxing their upper bodies and on tight muscles. Every muscle must be tight. Doing these stretches regularly makes it easier to surf without suffering from injuring. Stretches vary and are based on a lot of types of exercises that people should do. What is very important for professional surfers, according to the text?