Which of the following is NOT the result of a tornado?
A.Insects are unable to balance themselves.
B.It is difficult to breathe.
C.A tornado destroys everything on its path.
D.A tornado kills 120 people every time it comes.
第7题
A.一般LD与光纤的藕合效率比LED高
B.LED属于阀值器件
C.LED主要靠受激辐射效应发光
D.由于LED的线性比LD好,因此LED更适合高速传输系统
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