题目

Did you know that sixty per cent of your body weight is water? However, a loss of only two per cent of this water throughdehydration(脱水) during exercise can significantly affect your performance. The more you sweat, the more your exerciseperformance declines, unless you drink enough to replace your lossof fluids. When you lose too much water, you can overheat quite easily,especially in a warm environment.But this is not the only problemyou may face. Dehydration leads to your heart pumping muchfaster, which means exercise becomes more difficult and requiresmore effort. Despite the下列说法中，正确的是（　　）A．水是由2个氢元素和1个氧元素构成B．水是由2个氢原子和1个氧原子构成的C．水是由氢、氧两种元素组成的D．水分子是由氢元素和氧元素组成的