A:CH5CH2OH →170∘C浓H2SO4 CH2=CH2+H2O↑
B:CH5CHBrCH5+NaOH →△乙醇 CH5CH=CH2↑+NaBr+H2O
C:
D:2CH3OH →△浓硫酸 CH3OCH3+H2O
使用如图所示的装置匀速提起重物G,所用的拉力中( )