A: 耧车
B: 翻车
C: 筒车
D: 风力水车
如图,AC是电杆AB的一根拉线,测得BC=6米,∠ACB=52°,则拉线AC的长为( )
Are you alone? I just want a ______ word with you.
①若l⊂α,m⊂α,l∥β,m∥β,则α∥β;
②若l⊂α,l∥β,α∩β=m,则l∥m;
③若α∥β,l∥α,则l∥β;
④若l⊥α,m∥l,α∥β,则m⊥β.
其中真命题是____(写出所有真命题的序号).