题目

Dear Donna,Help! I’m a 15 —year — old high school student in New York, In eight months, I’m going to take an entrance exam. To prepare, I’m studying six hours a day. I want to do well, but I’m really stressed (焦虑不安的) these days. I can’t sleep. What can I do?Yours,MaryDear Mary,Many students around the world have the same problems as you. Here is some advice to help you deal with the stress (压力) .Good luck !1. Make a study plan for yourself, but don’t study too much in one day. You remember more by studying one hour each day for six days, than six hours in one day.下列各实例中（均不计空气阻力），机械能守恒的是（　　）A．做自由落体运动的小球B．跳伞员带着张开的降落伞匀速下降C．小球沿光滑圆弧槽滑下D．小球沿粗糙斜面匀速滑下