A:had done; had bee
B:could do; wa
C:could have done; wa
D:hadn’t done; had bee
如图装置常用来测定空气中氧气的含量.下列对该实验的认识中不正确的是( )
tóu jǐng
zhèng zhòng
lì shēng
jīng jù
sān cān
____
如图,DE是△ABC的中位线,F是DE的中点,CF的延长线交AB于点G,若△CEF的面积为12cm2,则S△DGF的值为( )