题目

Many people hurt their backs when they try to lift heavy things from the floor. It is easy to hurt your back muscle(肌肉) when you try to pick up a heavy thing. However, there is a correct way to lift things from the floor. If you pick up heavy things correctly, you probably will not hurt your back.    To lift something from the floor correctly, first bend (弯曲) your knees and lower yourself. Keep your back straight. Do not bent over, from your waist (腰) keep your back and hips (臀部) and waist in a line. If you bent over, the muscles in your lower back can became hurt very在人的体细胞和卵细胞中的染色体数分别是（ ）A．23对23条B．0条23条C．23条23条D．23条23对