(____) I'm looking out of the window.
(____) Some children are making a snowman.
(____) In this photo,we are in the mountains.
(____) The wind is blowing and the sun is shining.
(____) I am having a lovely time.
下列命题的逆命题一定成立的个数是( )
①对顶角相等;②同位角相等,两直线平行;③若a=b,则|a|=|b|;④若x=3,则x2﹣3x=0.