听力原文： Good morning. I' d like to welcome you to your first yoga class. Before we begin our exercises, it is important that we undid a few facts about yoga. First of all, it is not a religion. Yoga is a way of life and can serve only to improve your present way of life. Yoga is an exact science and a delicate art. Secondly, be as methodical and mechanical as possible. Never tug, swain, or pull strenuously. Forcing will cause your body to resist and will actually slow down or even prevent your progress. Go gently, stretch up to the point where it would start to hurt, and then stop immediately. The key is proper breathing through the nostrils with the mouth shut. Many times it is best to practice alone in a well-ventilated room, preferably wearing little or no clothing. Never practice on a full stomach because an empty one permits greater flexibility. Exercise will benefit your general health. Yoga cannot add or subtract pounds from your figure; only eating more or less food, that is, increasing or decreasing your caloric intake, can do that. Always member that diet affects weight, while exercise affects shape. Neither can do the job of the other. Now, Let's begin with our first yoga exercise. According to the speaker, yoga should NOT be described as ______