建沼气池拌制混凝土的材料有哪些？
参考答案：
建沼气池拌制混凝土的材料是水泥、砂、水和石子。
架空导线的种类有（）。
A．裸导线
B．避雷线
C．绝缘导线
D．接地线
You are a salesman in a pharmacy company. Write a letter to Mr. Wang, one of your customers, to introduce a new medicine to him.
Do not sign your own name at the end of the letter. Use "Li Ming" instead.
Do not write the address.
