Dear student,
Symmetry is defined as a balanced and a proportionate similarity which is found in two halves of an object, that is, one-half is the mirror image of the other half.
In simple words the imaginary line or axis along which you can fold a figure to obtain the symmetrical halves is called the line of symmetry.
So, we reach to the conclusion that the - c figure has a line of symmetry because in the figure c the shape is being divided into equal parts with equal number of blocks.
Regards!!