光纤通信系统按传输信号的类型可分为：（）和光纤数字系统。
参考答案：光纤模拟通信系统
“皮肤咖啡牛奶色斑”可见于（）
A.玫瑰糠疹
B.神经纤维瘤病
C.恶性黑素瘤
D.太田痣
E.皮内痣
It was reported that six _____ including a boy.
A．waskilled
B．werekilled
C．waskilling
D．hadkilled
