下列有机反应属于加成反应的是( )
A:2CH3CH2OH+2Na﹣→2CH3CH2ONa+H2↑
B:CH3COOCH2CH3+H2OCH3COOH+CH3CH2OH
C:CH2═CH2+Br2﹣→CH2BrCH2Br
D:2CH3CHO+O22CH3COOH
34 ×8=
2.5﹣ 12 =
15÷1%=
23 + 34 =
75 × 1021 =
0.3× 56 =
35 ÷ 910 =
1÷ 78 =
6﹣ 67 =
1﹣1× 13 =
在使用光学显微镜时,下列叙述正确的是( )