A:装置①:制取氧气(发生装置)
B:装置②:由a进气收集O2
C:装置③:制取氧气(发生装置)
D:装置④:排空气法收集氧气时用带火星的木条验满
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By mentioning Muhammad Ali's words, the author intends to tell us that.
若圆C:x2+y2+2x﹣4y+3=0关于直线2ax+by+6=0对称,则由点(a,b)向圆C所作切线长的最小值是( )