光纤通信的特点:(1)通信容量大、传输距离远;(2)信号干扰小、保密性能好;(3)抗电磁干扰、传输质量佳;(4)光纤尺寸小、重量轻,便于铺设和运输;(5)无辐射,难于窃听;
从方框中选词并用其适当形式填空
wear sing hear watch help
(1)Tony likes music and he likes ____.
(2)Be quiet! Can you ____ someone is singing a song?
(3)Tom’s aunt always ____ T- shirts.
(4)The family like ____ TV at home together.
(5)Li Lei always ____ others.
下图是某同学探究性学习中使用的一幅地图。据这幅地图的内容判断,该同学的探究题目应是( )
已知向量a→=(2,-3,5)与向量b→=(-4,x,y)平行,则x,y的值分别是( )