We can combine the convex lens and the concave lens and the combined lens is called a convexo-concave or concavo-convex lens for which one side is convex and other side is concave. Since, convex and concave lenses are $3-$ dimensional object because each one is formed from two spheres (a three-dimensional object) and so the combined object is also a $3-$ dimensional object.
More details:
$1)$ https://physics.stackexchange.com/questions/217757/difference-between-convexo-concave-and-concavo-convex-lenses
$2)$ https://www.youtube.com/watch?v=4zuB_dSJn1Y
Hence, $(A)$ and $(B)$ are eliminated and $(C)$ is correct.
Also, the texture of this $3-$ dimensional object is smooth because it is having continuous even surface and not having bumps, holes, ridges or any rough surface.
A smooth surface has a well-defined tangent plane at every point of the surface.
Now, option $(D)$ may be correct depends on what "edge" implies here. If you consider the curved edge (like a self loop in graphs) as an edge then option $(D)$ is also correct because consider a cylinder which has $2$ curved edges, $1$ curved surface, $2$ flat faces and no corners but if you consider the edge as an straight line then for a finite three-dimensional object, option $(D)$ is wrong because where at least two lines or straight edges meet, it creates a corner and according to the definition of smoothness, it should not have a sudden rise or fall and so it will not be a smooth object and so if edge means straight edges then $(D)$ is wrong.
Since question implies only one option is correct, so you can either go with $(C)$ or $(D).$
Note:
1. A $3-$ dimensional object can neither be convex nor concave.
For example: Hyperbolic Paraboloid ( https://www.wolframalpha.com/input?i=f%28x%2Cy%29%3Dxy )
(More details)
2. Both Convex and Concave: https://www.geogebra.org/3d/q4ghpzae
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Edit:
1. In the revised answer key, answer has not been changed, So, it might has been assumed edges as straight edges, not curved edges and probably we could challenge this question too if we are challenging the above question because here also we can assume so. But they should have to define edges like it is mentioned here in comments.
- There are some issues if we assume an “edge” as “curved edge” here like whether the object would be “Smooth” or not and what if, object is “infinite” ? Can we see an infinite object ? These questions are addressed here.
- With the use of Differential Geometry, we can prove that infinite Cylinder $x^2+y^2=1;z \in \mathbb{R}$ is smooth and also as mentioned in comments, this cylinder is diffeomorphic to finite length cylinder and Diffeomorphism preserves the smoothness. So, mathematically, Option $(D)$ should also be correct.
- There are some books like "Elementary Differential Geometry" by Andrew Pressley to understand the proof and mentioned notations and definitions and also, you can watch documentary “A Trip to Infinity” if you have interest and Netflix subscription to understand infinity.
