The correct option is B A convex lens
We cannot look through a mirror as one of its surfaces is polished. So, we must use a lens for reading small letters in a dictionary.
We know that a convex lens is commonly known as a magnifying glass. This is because the image formed by a convex lens is bigger in size for a nearby object.
Whereas, the image formed by a concave lens is always virtual, erect and diminished.
Therefore, we should use a convex lens for reading small letters found in a dictionary.