题目

Mr Brown was going away for a week. Before he left, he said to his son, if anyone asks for me, you can tell him that your father has been out for doing something, and will be back in a week, then be sure to ask him to sit down for a cup of tea.OK, Dad, said his son. But he was afraid his son couldn't remember this, he wrote these words down on a piece of paper and gave it to him. His son put it into his small pocket, took it out and looked at it every now and then. Four days passed, but no one came to see his father. The boy thought that there was no man to come and that the piece of p元素的种类取决于原子的核电荷数或质子数；元素的化学性质取决于原子的 ．在化学反应中，元素种类和质量都不会 ．