Time to exercise 1. An old Chinese proverb says that one will never find it difficult to do anything until he has experienced it. 2. Motion is absolute while stagnation is relative 3. Mechanical energy is changed into electric energy,which in turn is changed into mechanical energy. 4. Fine grains of dust can reflect blue light,which coarse grains of dust can not. 5. Matter is composed of molecules that are composed of atoms. 6. When the solution is saturated,no more solute will be dissolved. 7. The water vapor makes it possible,though without the dust it could not condense and fall as rain,watering crops and making them grow. 8. The present "packing density"of 2.5 million bits of information per square inch can be increased in the future. Time to exercise 1. An old Chinese proverb says that one will never find it difficult to do anything until he has experienced it. 2. Motion is absolute while stagnation is relative. 3. Mechanical energy is changed into electric energy, which in turn is changed into mechanical energy. 4. Fine grains of dust can reflect blue light, which coarse grains of dust can not. 5. Matter is composed of molecules that are composed of atoms. 6. When the solution is saturated, no more solute will be dissolved. 7. The water vapor makes it possible, though without the dust it could not condense and fall as rain, watering crops and making them grow. 8. The present “packing density” of 2.5 million bits of information per square inch can be increased in the future