单项选择题
A.7~8μm B.9~10μm C.11~12μm D.12~13μm
A.50μm B.100μm C.125μm D.150μm
A.n1＝n2 B.n1＜n2 C.n1≥n2 D.n1＞n2
A.包层 B.内外层间 C.纤芯 D.纤芯与包层间
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