Two different cross sections are taken parallel to the base of a three-dimensional figure. the theo cross sections are the same shape but are not congruent. what is the three-dimensional figure?

Same shape => similar.

The sections could be either great or smaller in area.

The possible figures could be:
1. A cone (all sections are circles)
2. A truncated cone (all sections are circles)
3. A hemisphere (all sections are circles)
4. A pyramid of any base (triangle, square, pentagon,)
5. A truncated pyramid of any base (triangle, square, pentagon,)
There are still other less conventional shapes, but I suppose the above options should suffice.

Your pictures are upside down