A:They are talking about how to make salad.
B:They are taking an order in a restaurant.
C:They are eating salad.
请到答下列问题:
下列哪种仪器可以扩大我们的观察范围( )
已知直线 l,m;平面α,β;且l⊥α,m⊂β,给出下列四个命题:①若α∥β,则l⊥m;②若l⊥m,则α∥β;③若α⊥β,则l∥m;④若l∥m,则α⊥β其中正确的命题是( )
解一元二次方程x2-2x-5=0,结果正确的是( )