以其外形、数量、质量等客观存在来证明待证事实的是()。
参考答案：物证
—Who is knocking at the door?
—It ______ be Miss Zhang. Because she has just gone to Japan.[ ]
A. mustn't
B. can't
C. may not
D. needn't
线路爬行量大于（）时应及时整正。
A、20mm
B、30mm
C、40mm
