If you draw a diagonal line from corner to corner of a parallelogram, that is a line of symmetry.
http://wiki.answers.com/Q/Why_parallelogram_has_no...

Parallelograms do not have any lines of symmetry. Parallelograms
http://www.chacha.com/question/howmanylinesofs...

A line of symmetry is a line that divides a figure into two halves that are mirror image of each other. The line of symmetry forms a symmetrical figure as it cuts the figure exactly
http://answers.ask.com/Science/Mathematics/what_is...

1. Determine where the line is within the shape. Highlight or draw the line. 2. Use a fold test on the line to see if the line has symmetry. Fold the shape onto itself with the line
http://www.ehow.com/how_8700808_testlinesymmetry...
