Cone....
A shape cannot have only one side because it would not be closed. A shape must have at least three sides to be a closed figure (no "gaps")
the shape has 1 side of symmetry
It is not possible to have 1 parallel side since it must be parallel to another side. A four sided shape with 1 PAIR of parallel sides is a trapezium (or trapezoid).
The Mobius Strip. It is a 3-Dimensional Object, that you can make with paper in your very own home, that has only 1 side, and 1 boundary. It is hard to describe, but it does exist. look for images or try it yourself!While it is commonly believed that Circles and Spheres have only 1 side, they this is technically not true. A sphere has 2 sides, the inside and out. (Unless you are talking about a solid ball). A circle, is still under much debate, as the definition of "side" is not fully universal. Some would say a circle has one side, some would say it has an infinite number of sides, while still others believe it has no sides. The only TRUE one sided shape, is the Mobius Strip.
A semicircle is one shape fitting this description.
Not sure how you can have only one parallel side. What is it parallel to?
Cone....
A shape cannot have only one side because it would not be closed. A shape must have at least three sides to be a closed figure (no "gaps")
a circle
No shape has only 1 parallel side. A trapezoid is a 4-sided shape, or quadrilateral, with only 2 parallel sides; it does not necessarily have to have 2 right angles. (In the UK a trapezoid is called a trapezium.) In North America, a trapezium is a quadrilateral with 0 (no) parallel sides.
a circle
A semicircle.
If you mean one pair of parallel lines, then you're talking about a trapezoid.
A two dimentional shape with 1 side and 1 vertex.
A vertical line
A sphere