通常情况下，紫外光区与可见光区的波长范围分别是
A. 200nm-400nm; 400nm-800nm
B. 200nm-400nm; 400nm-600nm
C. 100nm-360nm; 400nm-800nm
D. 100nm-360nm; 360nm-600nm
当吸光度A=0时，则透光率T/%=()
A. 50
B. 20
C. 1
D. 100
--- Tom graduated from college at a very young age.--- Oh, he ______ have been a very smart boy then.
A. could
B. should
C. might
D. must
--- I don't mind telling you what I know.--- You ______. I'm not asking you for it.
A. mustn't
B. may not
C. can't
D. needn't
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