What is the purpose in writing this text?
A.Telling people how serious the damage caused by landslides is.
B.Telling people that sending workers to stabilize mountainsides is a risky job.
C.Introducing a product that can be used to stabilize mountainsides.
D.Showing people how to use a new product.
第4题
A.量子通信将被称为唯一能提供安全的保密通信手段
B.目前,量子通信是海上、高空、边远地区和野外的主要通信手段
C.卫星通信系统实际上是一种微波通信
D.卫星通信是以卫星作为中继站转发微波信号,在多个地面站之间进行微波信号的传输
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