Jack: I'm in Shandong.It's 21℃ today.It's____.I can go to the playground.
已知四边形ABCD是菱形,若对角线AC⇀=1,2,BD⇀=-2,λ,则λ的值是( )
在人体的胚胎发育过程中,胎儿发育的场所是( )