单项选择题
A.5r1 B.1/5r2 C.1/2r1 D.1/4r1
A.60° B.80° C.100° D.120°
A.硫 B.磷 C.锰 D.铅
A.300~400℃ B.400~500℃ C.500~600℃ D.600~700℃
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