For image magnification, one needs at least
A). Two convex lenses
B). One concave and one convex lens
C). One concave lens
D). One convex lens

Hint: Lenses form images at the point where two rays originated from the body meet after passing through the lens. For image magnification, the rays passing through the focal centre of the lens and one other ray, both originated from the body, should meet at a point where the height of the image is greater than the object length.

Complete step-by-step solution:
Convex lenses are majorly used to provide us with the magnified image of an object. It creates an erect, enlarged virtual image of the small object. The working of convex lenses can be illustrated using the following diagram:

Here, let AB be the object to be viewed. The image of this object is magnified, erect and is virtually made by the convex lens. This image is $A’B’$. We see this enlarged image.
One convex lens is sufficient to create an appropriately large image of an object. But if the object is very very small, two of such convex lenses are required to create a sufficiently large image so that it can be viewed clearly.
Thus, if the object is small we need only one convex lens to make the magnified image. But if the object is very small we need two such convex lenses to make the appropriate magnified image.
Hence, the answer is option (a).

Note: Convex lenses form different types of image for objects kept at different distances. For the purpose of image magnification, we need to keep the object within the focal length of the lens. For this distance the object formed is magnified and erect.