已知a、b是两条不重合的直线，α、β、γ是三个两两不重合的平面，给出下列四个命题：

①若a⊥α，a⊥β，则α∥β；

②若α⊥γ，β⊥γ，则α∥β；

③若α∥β，a⊂α，b⊂β，则a∥b；

④若α∥β，α∩γ=a，β∩γ=b，则a∥b．

其中正确命题的序号有 ______．

Which statement is TRUE concerning the gooseneck（）.

A.It is a sailing maneuver which brings the vessel's head through the wind

B.It connects the boom to the mast and allows the boom to swing freely

C.It is a sailing condition where there is a loss of air flow over the sails

D.None of the above