Step-by-step answer:
First we need to know the properties of the given figures.
There are many ways to describe a parallelogram. Here we will use the simple description that
"A parallelogram is a convex quadrilateral with opposite sides equal and parallel."
If we take pencil and paper to construct two parallel and equal lines, and join the corresponding points, we can only get a parallelogram (as long as the figure is convex.
Similarly, if we draw four equal lines to draw a parallelogram, we can only get a rhombus. Therefore a rhombus is a parallelogram with all four sides equal.
See the Venn diagram attached.
Note
(in fact, the minimum definition of a rhombus is "a parallelogram with two adjacent sides equal")
