光隔离器的作用是（）
A.调节光信号的功率大小
B.保证光信号只能正向传输
C.分离同向传输的各路光信号
D.将光纤中传输的监控信号隔离开
参考答案：A
积极支持本国工人运动，并为支援希腊人民的独立战争事业而献身的浪漫主义诗人是
A．拜伦
B．雪莱
C．歌德
D．巴尔扎克
Which of the following most accurately describes the shapes of the average variable cost (AVC) and average total cost (ATC) curves（）
A. The AVC and ATC curves are both U-shaped.
B. The AVC and ATC curves both decrease initially, and then flatten.
C. The AVC curve is U-shaped whereas the ATC curve declines initially then flattens.
