-- I had a pleasant winter vacation with my family in the north.
-- ______.
A:Oh, that's nice of you
B:Enjoy yourself
C:Well done
D:Glad to hear that
设α、β是两个不同的平面,l是一条直线,以下命题:①若l⊥α,α⊥β,则l⊂β;②若l∥α,α∥β,则l⊂β; ③若l⊥α,α∥β,则l⊥β;④若l∥α,α⊥β,则l⊥β。
其中正确命题的个数是( )
(Ⅰ)求角A的大小;
(Ⅱ)若a=2,b=2 3 ,求△ABC的面积.