About the importance of health, nobody can explain ____ (well) than your doctor. They are the people who really know the importance of keeping fit and healthy. Every time I put on ____ extra pound, my doctor will remind me about what is happening ____ my body. We may look healthy but we don’t know ____ (clear) what is happening inside. And there are many different ways we can make sure that we are as ____ (health) inside as we are outside. The first and easiest step is keeping a good ____ balanced diet. Next is sleeping well. Sleep early. Make sure you get your nine hours’ sleep. Do not skip your breakfast. It is one of the most important ____ (meal) of the day. Exercise every day. Go for a swim, or walk, or just play football or tennis. Try your best not to have too much stress because it’s very ____ (harm) to your health. Remember to keep ____ (wash) your hands, and then you won’t catch any infections(传染病). And getting away from your bad habits ____ (be) important too.

已知一个空瓶子装满水后的总质量为300g，在装满水的瓶子中放入一个小石块，溢出水后其总成量为320g，取出石块后，剩余的水和瓶子的总质量为290g．（不计取出石块的过程中带走的水）则石块的质量为____g，石块的密度为____g/cm³。（ρ_水=1.0×10³kg/m³）