A:19.7 mm
B:19.8 mm
C:20 mm
D:20.05 mm
—Yes. We should pay attention to the safety all the time.
如图,在△ABC中,D、E分别是边AB、AC的中点,延长BC至点F,使得CF=12BC,连结CD、DE、EF.
(1)求证:四边形CDEF是平行四边形.
(2)若四边形CDEF的面积为8,则△ABC的面积为多少.
伏尔加河、贝加尔湖的特点分别是( )