star
triangle
Parallelogram
Pentagon
A rectangle and a square, which is also a rectangle.
an equilateral triangle
octagon
Impossible.
Square
If your asking what shape has three lines of symmetry, your answer would be an equilateral triangle. You can tell how many lines of symmetry a shape that has all angles of the same measure has by looking at it's angles. Ex., pentagon has five angles--five lines of symmetry; octagon has eight angles, eight lines of symmetry; etc.
An equilateral triangle has 3 equal acute angles of 60 degrees and it has 3 lines of symmetry.
An irregular quadrilateral.