A:did we hear
B:we heard
C:had we heard
D:we have heard
①生命的意义不在于长短,而在于对社会的贡献
②要漠视自己的生命,视生命为身外之物
③珍爱他人的生命,就要放弃自己的生命
④在生命的接续中,人类的精神也在不断传承
Jack's made few mistakes in his exam, ______?
如图,在△ABC中,D、E分别是边AB、AC的中点,点F是BC延长线上一点,且CF=12BC,连结CD、EF.求证:CD=EF.