单项选择题

B

Before any period of exercise it is well worth spending two or three minutes warming up with a series of simple stretching exercises. This not only helps your joints (关节) to move easily but also pre-pares all your muscle groups for more energetic activity. It is rather like a cat stretching itself before it springs into action. Here are four movements to do in an easy and unhurried way, gently stretching each action without forcing it. Repeat each movement ten times, breathing normally throughout. Ⅰ. Standing with your feet apart, push both arms out straight in front of you, fingertips touching. Raise them above your head, then down to the sides pushing each arm backwards at the same time. Ⅱ. Standing with your feet apart, and hands on hips (臀部). Tip your head back and look straight up to the ceiling. Roll your head round slowly to face the right, then the floor, then the left, and finally up at the ceiling again. Repeat in the other direction. Ⅲ. Standing with your feet apart and hands on your sides, lean first to the right and then to the left, sliding the hand down the side of the leg. Ⅳ. Standing feet apart and arms out straight in front, with your eyes fixed on your right hands, as far as it will go. Return it to the front and repeat with the left arm.

Doing exercise 1I mainly trains the joints of your ______.