A． Prompt delivery of the goods before Christmas is the most important.

B．Top priority should be given to the competitive and reasonable price of the goods

C．During Christmas, there will be a shopping craze for goods with good quality.

D． Nothing is more important than the quality and price of the goods for Christmas

光纤通信技术中，光放大器的工作原理是？（）

A.自发吸收

B.受激辐射

C.受激吸收

D.自发辐射