阅读下面短文，将文中划线句子译成中文。
　　Some kids in boarding school often like to talk with their roommates. ____ They won’t stop talking until someone comes to stop them. This is the reason why many of them are sleepy in class the next day. Lack of (缺乏) sleep is bad for their health. Growth hormones (生长激素) are very important if one is to grow taller. ____ The body makes the most hormones between 10 p.m. and 2 a.m. While you are asleep. ____ This means that if you don’t get to sleep at the time, you won’t grow taller.

有一恒力F施于质量为m₁的物体上，产生加速度a₁；若此力施于质量m₂的物体上，产生加速度a₂，若此力施于质量为m₁+m₂的物体上，产生的加速度为（   ）